diff --git a/doc/api/errors.md b/doc/api/errors.md
index c908846d5471aa..2fc655b3c55e8c 100644
--- a/doc/api/errors.md
+++ b/doc/api/errors.md
@@ -1683,6 +1683,12 @@ A non-context-aware native addon was loaded in a process that disallows them.
 
 A given value is out of the accepted range.
 
+<a id="ERR_PACKAGE_IMPORT_NOT_DEFINED"></a>
+### `ERR_PACKAGE_IMPORT_NOT_DEFINED`
+
+The `package.json` ["imports" field][] does not define the given internal
+package specifier mapping.
+
 <a id="ERR_PACKAGE_PATH_NOT_EXPORTED"></a>
 ### `ERR_PACKAGE_PATH_NOT_EXPORTED`
 
@@ -2533,3 +2539,4 @@ closed.
 [vm]: vm.html
 [self-reference a package using its name]: esm.html#esm_self_referencing_a_package_using_its_name
 [define a custom subpath]: esm.html#esm_subpath_exports
+["imports" field]: esm.html#esm_internal_package_imports
diff --git a/doc/api/esm.md b/doc/api/esm.md
index cbba5fc41ec43a..268ccff5f99f7c 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -546,6 +546,43 @@ and in a CommonJS one. For example, this code will also work:
 const { something } = require('a-package/foo'); // Loads from ./foo.js.
 ```
 
+### Internal package imports
+
+In addition to the `"exports"` field it is possible to define internal package
+import maps that only apply to import specifiers from within the package itself.
+
+Entries in the imports field must always start with `#` to ensure they are
+clearly disambiguated from package specifiers.
+
+For example, the imports field can be used to gain the benefits of conditional
+exports for internal modules:
+
+```json
+// package.json
+{
+  "imports": {
+    "#dep": {
+      "node": "dep-node-native",
+      "default": "./dep-polyfill.js"
+    }
+  },
+  "dependencies": {
+    "dep-node-native": "^1.0.0"
+  }
+}
+```
+
+where `import '#dep'` would now get the resolution of the external package
+`dep-node-native` (including its exports in turn), and instead get the local
+file `./dep-polyfill.js` relative to the package in other environments.
+
+Unlike the exports field, import maps permit mapping to external packages
+because this provides an important use case for conditional loading and also can
+be done without the risk of cycles, unlike for exports.
+
+Apart from the above, the resolution rules for the imports field are otherwise
+analogous to the exports field.
+
 ### Dual CommonJS/ES module packages
 
 Prior to the introduction of support for ES modules in Node.js, it was a common
@@ -1577,10 +1614,11 @@ The resolver can throw the following errors:
   or package subpath specifier.
 * _Invalid Package Configuration_: package.json configuration is invalid or
   contains an invalid configuration.
-* _Invalid Package Target_: Package exports define a target module within the
-  package that is an invalid type or string target.
+* _Invalid Package Target_: Package exports or imports define a target module
+  for the package that is an invalid type or string target.
 * _Package Path Not Exported_: Package exports do not define or permit a target
   subpath in the package for the given module.
+* _Package Import Not Defined_: Package imports do not define the specifier.
 * _Module Not Found_: The package or module requested does not exist.
 
 <details>
@@ -1592,11 +1630,14 @@ The resolver can throw the following errors:
 > 1. If _specifier_ is a valid URL, then
 >    1. Set _resolvedURL_ to the result of parsing and reserializing
 >       _specifier_ as a URL.
-> 1. Otherwise, if _specifier_ starts with _"/"_, then
->    1. Throw an _Invalid Module Specifier_ error.
-> 1. Otherwise, if _specifier_ starts with _"./"_ or _"../"_, then
+> 1. Otherwise, if _specifier_ starts with _"/"_, _"./"_ or _"../"_, then
 >    1. Set _resolvedURL_ to the URL resolution of _specifier_ relative to
 >       _parentURL_.
+> 1. Otherwise, if _specifier_ starts with _"#"_, then
+>    1. Set _resolvedURL_ to the result of
+>       **PACKAGE_INTERNAL_RESOLVE**(_specifier_, _parentURL_).
+>    1. If _resolvedURL_ is **null** or **undefined**, throw a
+>       _Package Import Not Defined_ error.
 > 1. Otherwise,
 >    1. Note: _specifier_ is now a bare specifier.
 >    1. Set _resolvedURL_ the result of
@@ -1634,7 +1675,7 @@ The resolver can throw the following errors:
 > 1. If _packageSubpath_ contains any _"."_ or _".."_ segments or percent
 >    encoded strings for _"/"_ or _"\\"_, then
 >    1. Throw an _Invalid Module Specifier_ error.
-> 1. Set _selfUrl_ to the result of
+> 1. Let _selfUrl_ be the result of
 >    **SELF_REFERENCE_RESOLVE**(_packageName_, _packageSubpath_, _parentURL_).
 > 1. If _selfUrl_ isn't empty, return _selfUrl_.
 > 1. If _packageSubpath_ is _undefined_ and _packageName_ is a Node.js builtin
@@ -1657,8 +1698,11 @@ The resolver can throw the following errors:
 >       1. If _pjson_ is not **null** and _pjson_ has an _"exports"_ key, then
 >          1. Let _exports_ be _pjson.exports_.
 >          1. If _exports_ is not **null** or **undefined**, then
->             1. Return **PACKAGE_EXPORTS_RESOLVE**(_packageURL_,
->                _packageSubpath_, _pjson.exports_).
+>             1. Let _resolved_ be the result of  **PACKAGE_EXPORTS_RESOLVE**(
+>                _packageURL_, _packageSubpath_, _pjson.exports_).
+>             1. If _resolved_ is **null** or **undefined**, throw a
+>                _Package Path Not Exported_ error.
+>             1. Return _resolved_.
 >       1. Return the URL resolution of _packageSubpath_ in _packageURL_.
 > 1. Throw a _Module Not Found_ error.
 
@@ -1679,8 +1723,11 @@ The resolver can throw the following errors:
 >       1. If _pjson_ is not **null** and _pjson_ has an _"exports"_ key, then
 >          1. Let _exports_ be _pjson.exports_.
 >          1. If _exports_ is not **null** or **undefined**, then
->             1. Return **PACKAGE_EXPORTS_RESOLVE**(_packageURL_, _subpath_,
->                _pjson.exports_).
+>             1. Let _resolved_ be the result of **PACKAGE_EXPORTS_RESOLVE**(
+>                _packageURL_, _subpath_, _pjson.exports_).
+>             1. If _resolved_ is **null** or **undefined**, throw a
+>                _Package Path Not Exported_ error.
+>             1. Return _resolved_.
 >       1. Return the URL resolution of _subpath_ in _packageURL_.
 > 1. Otherwise, return **undefined**.
 
@@ -1693,12 +1740,18 @@ The resolver can throw the following errors:
 >       not starting with _"."_, throw an _Invalid Package Configuration_ error.
 >    1. If _pjson.exports_ is a String or Array, or an Object containing no
 >       keys starting with _"."_, then
->       1. Return **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_,
->          _pjson.exports_, _""_).
+>       1. Let _resolved_ be the result of  **PACKAGE_TARGET_RESOLVE**(
+>          _packageURL_, _pjson.exports_, _""_, **false**, _defaultEnv_).
+>       1. If _resolved_ is **null** or **undefined**, throw a
+>          _Package Path Not Exported_ error.
+>       1. Return _resolved_.
 >    1. If _pjson.exports_ is an Object containing a _"."_ property, then
 >       1. Let _mainExport_ be the _"."_ property in _pjson.exports_.
->       1. Return **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_,
->          _mainExport_, _""_).
+>       1. Let _resolved_ be the result of **PACKAGE_TARGET_RESOLVE**(
+>          _packageURL_, _mainExport_, _""_, **false**, _defaultEnv_).
+>       1. If _resolved_ is **null** or **undefined**, throw a
+>          _Package Path Not Exported_ error.
+>       1. Return _resolved_.
 >    1. Throw a _Package Path Not Exported_ error.
 > 1. Let _legacyMainURL_ be the result applying the legacy
 >    **LOAD_AS_DIRECTORY** CommonJS resolver to _packageURL_, throwing a
@@ -1712,8 +1765,8 @@ The resolver can throw the following errors:
 >    1. Set _packagePath_ to _"./"_ concatenated with _packagePath_.
 >    1. If _packagePath_ is a key of _exports_, then
 >       1. Let _target_ be the value of _exports\[packagePath\]_.
->       1. Return **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_, _target_,
->          _""_, _defaultEnv_).
+>       1. Return **PACKAGE_TARGET_RESOLVE**(_packageURL_, _target_,
+>          _""_, **false**, _defaultEnv_).
 >    1. Let _directoryKeys_ be the list of keys of _exports_ ending in
 >       _"/"_, sorted by length descending.
 >    1. For each key _directory_ in _directoryKeys_, do
@@ -1721,22 +1774,28 @@ The resolver can throw the following errors:
 >          1. Let _target_ be the value of _exports\[directory\]_.
 >          1. Let _subpath_ be the substring of _target_ starting at the index
 >             of the length of _directory_.
->          1. Return **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_, _target_,
->             _subpath_, _defaultEnv_).
-> 1. Throw a _Package Path Not Exported_ error.
+>          1. Return **PACKAGE_TARGET_RESOLVE**(_packageURL_, _target_,
+>             _subpath_, **false**, _defaultEnv_).
+> 1. Return **null**.
 
-**PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_, _target_, _subpath_, _env_)
+**PACKAGE_TARGET_RESOLVE**(_packageURL_, _target_, _subpath_, _internal_, _env_)
 
 > 1. If _target_ is a String, then
->    1. If _target_ does not start with _"./"_ or contains any _"node_modules"_
->       segments including _"node_modules"_ percent-encoding, throw an
->       _Invalid Package Target_ error.
+>    1. If _target_ contains any _"node_modules"_ segments including
+>       _"node_modules"_ percent-encoding, throw an _Invalid Package Target_
+>       error.
+>    1. If _subpath_ has non-zero length and _target_ does not end with _"/"_,
+>       throw an _Invalid Module Specifier_ error.
+>    1. If _target_ does not start with _"./"_, then
+>       1. If _target_ does not start with _"../"_ or _"/"_ and is not a valid
+>          URL, then
+>          1. If _internal_ is **true**, return **PACKAGE_RESOLVE**(
+>             _target_ + _subpath_, _packageURL_ + _"/"_)_.
+>       1. Otherwise throw an _Invalid Package Target_ error.
 >    1. Let _resolvedTarget_ be the URL resolution of the concatenation of
 >       _packageURL_ and _target_.
 >    1. If _resolvedTarget_ is not contained in _packageURL_, throw an
 >       _Invalid Package Target_ error.
->    1. If _subpath_ has non-zero length and _target_ does not end with _"/"_,
->       throw an _Invalid Module Specifier_ error.
 >    1. Let _resolved_ be the URL resolution of the concatenation of
 >       _subpath_ and _resolvedTarget_.
 >    1. If _resolved_ is not contained in _resolvedTarget_, throw an
@@ -1748,22 +1807,48 @@ The resolver can throw the following errors:
 >    1. For each property _p_ of _target_, in object insertion order as,
 >       1. If _p_ equals _"default"_ or _env_ contains an entry for _p_, then
 >          1. Let _targetValue_ be the value of the _p_ property in _target_.
->          1. Return the result of **PACKAGE_EXPORTS_TARGET_RESOLVE**(
->             _packageURL_, _targetValue_, _subpath_, _env_), continuing the
->             loop on any _Package Path Not Exported_ error.
->    1. Throw a _Package Path Not Exported_ error.
+>          1. Let _resolved_ be the result of **PACKAGE_TARGET_RESOLVE**(
+>             _packageURL_, _targetValue_, _subpath_, _internal_, _env_)
+>          1. If _resolved_ is equal to **undefined**, continue the loop.
+>          1. Return _resolved_.
+>    1. Return **undefined**.
 > 1. Otherwise, if _target_ is an Array, then
->    1. If _target.length is zero, throw a _Package Path Not Exported_ error.
+>    1. If _target.length is zero, return **null**.
 >    1. For each item _targetValue_ in _target_, do
->       1. If _targetValue_ is an Array, continue the loop.
->       1. Return the result of **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_,
->          _targetValue_, _subpath_, _env_), continuing the loop on any
->          _Package Path Not Exported_ or _Invalid Package Target_ error.
->    1. Throw the last fallback resolution error.
-> 1. Otherwise, if _target_ is _null_, throw a _Package Path Not Exported_
->    error.
+>       1. Let _resolved_ be the result of **PACKAGE_TARGET_RESOLVE**(
+>          _packageURL_, _targetValue_, _subpath_, _internal_, _env_),
+>          continuing the loop on any _Invalid Package Target_ error.
+>       1. If _resolved_ is **undefined**, continue the loop.
+>       1. Return _resolved_.
+>    1. Return or throw the last fallback resolution **null** return or error.
+> 1. Otherwise, if _target_ is _null_, return **null**.
 > 1. Otherwise throw an _Invalid Package Target_ error.
 
+**PACKAGE_INTERNAL_RESOLVE**(_specifier_, _parentURL_)
+
+> 1. Assert: _specifier_ begins with _"#"_.
+> 1. If _specifier_ is exactly equal to _"#"_ or starts with _"#/"_, then
+>    1. Throw an _Invalid Module Specifier_ error.
+> 1. Let _packageURL_ be the result of **READ_PACKAGE_SCOPE**(_parentURL_).
+> 1. If _packageURL_ is not **null**, then
+>    1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_packageURL_).
+>    1. If _pjson.imports is a non-null Object, then
+>       1. Let _imports_ be _pjson.imports_.
+>       1. If _specifier_ is a key of _imports_, then
+>          1. Let _target_ be the value of _imports\[specifier\]_.
+>          1. Return **PACKAGE_TARGET_RESOLVE**(_packageURL_, _target_,
+>             _""_, **true**, _defaultEnv_).
+>       1. Let _directoryKeys_ be the list of keys of _imports_ ending in
+>          _"/"_, sorted by length descending.
+>       1. For each key _directory_ in _directoryKeys_, do
+>          1. If _specifier_ starts with _directory_, then
+>             1. Let _target_ be the value of _imports\[directory\]_.
+>             1. Let _subpath_ be the substring of _target_ starting at the
+>                index of the length of _directory_.
+>             1. Return **PACKAGE_TARGET_RESOLVE**(_packageURL_, _target_,
+>                _subpath_, **true**, _defaultEnv_).
+> 1. Return **null**.
+
 **ESM_FORMAT**(_url_)
 
 > 1. Assert: _url_ corresponds to an existing file.
diff --git a/doc/api/modules.md b/doc/api/modules.md
index e8215a2ace67ed..bcac4a6bf88d41 100644
--- a/doc/api/modules.md
+++ b/doc/api/modules.md
@@ -160,7 +160,9 @@ require(X) from module at path Y
    a. LOAD_AS_FILE(Y + X)
    b. LOAD_AS_DIRECTORY(Y + X)
    c. THROW "not found"
-4. LOAD_SELF_REFERENCE(X, dirname(Y))
+4. If X begins with '#'
+   a. LOAD_INTERAL_IMPORT(X, Y)
+4. LOAD_SELF_REFERENCE(X, Y)
 5. LOAD_NODE_MODULES(X, dirname(Y))
 6. THROW "not found"
 
@@ -236,6 +238,15 @@ LOAD_PACKAGE_EXPORTS(DIR, X)
 12. Otherwise
    a. If RESOLVED is a file, load it as its file extension format. STOP
 13. Throw "not found"
+
+LOAD_INTERNAL_IMPORT(X, START)
+1. Find the closest package scope to START.
+2. If no scope was found or the `package.json` has no "imports", return.
+3. let RESOLVED =
+  fileURLToPath(PACKAGE_INTERNAL_RESOLVE(X, pathToFileURL(START)), as defined
+  in the ESM resolver.
+4. If RESOLVED is not a valid file, throw "not found"
+5. Load RESOLVED as its file extension format. STOP
 ```
 
 ## Caching
diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 921bcce2878706..d7b37048bb8163 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -21,7 +21,6 @@ const {
   NumberIsInteger,
   ObjectDefineProperty,
   ObjectKeys,
-  StringPrototypeSlice,
   StringPrototypeStartsWith,
   Symbol,
   SymbolFor,
@@ -1097,16 +1096,9 @@ E('ERR_INVALID_FILE_URL_PATH', 'File URL path %s', TypeError);
 E('ERR_INVALID_HANDLE_TYPE', 'This handle type cannot be sent', TypeError);
 E('ERR_INVALID_HTTP_TOKEN', '%s must be a valid HTTP token ["%s"]', TypeError);
 E('ERR_INVALID_IP_ADDRESS', 'Invalid IP address: %s', TypeError);
-E('ERR_INVALID_MODULE_SPECIFIER', (pkgPath, subpath, base = undefined) => {
-  if (subpath === undefined) {
-    return `Invalid package name '${pkgPath}' imported from ${base}`;
-  } else if (base === undefined) {
-    assert(subpath !== '.');
-    return `Package subpath '${subpath}' is not a valid module request for ` +
-      `the "exports" resolution of ${pkgPath}${sep}package.json`;
-  }
-  return `Package subpath '${subpath}' is not a valid module request for ` +
-      `the "exports" resolution of ${pkgPath} imported from ${base}`;
+E('ERR_INVALID_MODULE_SPECIFIER', (request, reason, base = undefined) => {
+  return `Invalid module "${request}" ${reason}${base ?
+    ` imported from ${base}` : ''}`;
 }, TypeError);
 E('ERR_INVALID_OPT_VALUE', (name, value) =>
   `The value "${String(value)}" is invalid for option "${name}"`,
@@ -1120,31 +1112,20 @@ E('ERR_INVALID_PACKAGE_CONFIG', (path, message, hasMessage = true) => {
   return `Invalid JSON in ${path} imported from ${message}`;
 }, Error);
 E('ERR_INVALID_PACKAGE_TARGET',
-  (pkgPath, key, subpath, target, base = undefined) => {
-    const relError = typeof target === 'string' &&
+  (pkgPath, key, target, isImport = false, base = undefined) => {
+    const relError = typeof target === 'string' && !isImport &&
       target.length && !StringPrototypeStartsWith(target, './');
-    if (key === null) {
-      if (subpath !== '') {
-        return `Invalid "exports" target ${JSONStringify(target)} defined ` +
-        `for '${subpath}' in the package config ${pkgPath} imported from ` +
-        `${base}.${relError ? '; targets must start with "./"' : ''}`;
-      }
-      return `Invalid "exports" main target ${target} defined in the ` +
-        `package config ${pkgPath} imported from ${base}${relError ?
-          '; targets must start with "./"' : ''}`;
-    } else if (key === '.') {
+    if (key === '.') {
+      assert(isImport === false);
       return `Invalid "exports" main target ${JSONStringify(target)} defined ` +
-      `in the package config ${pkgPath}${sep}package.json${relError ?
-        '; targets must start with "./"' : ''}`;
-    } else if (relError) {
-      return `Invalid "exports" target ${JSONStringify(target)} defined for '${
-        StringPrototypeSlice(key, 0, -subpath.length || key.length)}' in the ` +
-        `package config ${pkgPath}${sep}package.json; ` +
-        'targets must start with "./"';
+        `in the package config ${pkgPath}package.json${base ?
+          ` imported from ${base}` : ''}${relError ?
+          '; targets must start with "./"' : ''}`;
     }
-    return `Invalid "exports" target ${JSONStringify(target)} defined for '${
-      StringPrototypeSlice(key, 0, -subpath.length || key.length)}' in the ` +
-    `package config ${pkgPath}${sep}package.json`;
+    return `Invalid "${isImport ? 'imports' : 'exports'}" target ${
+      JSONStringify(target)} defined for '${key}' in the package config ${
+      pkgPath}package.json${base ? ` imported from ${base}` : ''}${relError ?
+      '; targets must start with "./"' : ''}`;
   }, Error);
 E('ERR_INVALID_PERFORMANCE_MARK',
   'The "%s" performance mark has not been set', Error);
@@ -1293,15 +1274,16 @@ E('ERR_OUT_OF_RANGE',
     msg += ` It must be ${range}. Received ${received}`;
     return msg;
   }, RangeError);
+E('ERR_PACKAGE_IMPORT_NOT_DEFINED', (specifier, packagePath, base) => {
+  return `Package import specifier "${specifier}" is not defined${packagePath ?
+    ` in package ${packagePath}package.json` : ''} imported from ${base}`;
+}, TypeError);
 E('ERR_PACKAGE_PATH_NOT_EXPORTED', (pkgPath, subpath, base = undefined) => {
-  if (subpath === '.') {
-    return `No "exports" main resolved in ${pkgPath}${sep}package.json`;
-  } else if (base === undefined) {
-    return `Package subpath '${subpath}' is not defined by "exports" in ${
-      pkgPath}${sep}package.json`;
-  }
+  if (subpath === '.')
+    return `No "exports" main defined in ${pkgPath}package.json${base ?
+      ` imported from ${base}` : ''}`;
   return `Package subpath '${subpath}' is not defined by "exports" in ${
-    pkgPath} imported from ${base}`;
+    pkgPath}package.json${base ? ` imported from ${base}` : ''}`;
 }, Error);
 E('ERR_REQUIRE_ESM',
   (filename, parentPath = null, packageJsonPath = null) => {
@@ -1419,7 +1401,7 @@ E('ERR_UNKNOWN_FILE_EXTENSION',
 E('ERR_UNKNOWN_MODULE_FORMAT', 'Unknown module format: %s', RangeError);
 E('ERR_UNKNOWN_SIGNAL', 'Unknown signal: %s', TypeError);
 E('ERR_UNSUPPORTED_DIR_IMPORT', "Directory import '%s' is not supported " +
-'resolving ES modules, imported from %s', Error);
+'resolving ES modules imported from %s', Error);
 E('ERR_UNSUPPORTED_ESM_URL_SCHEME', 'Only file and data URLs are supported ' +
   'by the default ESM loader', Error);
 
diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index 7a004eef59d29d..f093f316b4717a 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -21,6 +21,12 @@
 
 'use strict';
 
+// Set first due to cycle with ESM loader functions.
+module.exports = {
+  wrapSafe, Module, toRealPath, readPackageScope,
+  get hasLoadedAnyUserCJSModule() { return hasLoadedAnyUserCJSModule; }
+};
+
 const {
   ArrayIsArray,
   Error,
@@ -36,6 +42,7 @@ const {
   ReflectSet,
   RegExpPrototypeTest,
   SafeMap,
+  SafeSet,
   String,
   StringPrototypeIndexOf,
   StringPrototypeMatch,
@@ -89,19 +96,20 @@ const {
 const { validateString } = require('internal/validators');
 const pendingDeprecation = getOptionValue('--pending-deprecation');
 
-module.exports = {
-  wrapSafe, Module, toRealPath, readPackageScope,
-  get hasLoadedAnyUserCJSModule() { return hasLoadedAnyUserCJSModule; }
-};
-
-let asyncESM, ModuleJob, ModuleWrap, kInstantiated;
-
 const {
   CHAR_FORWARD_SLASH,
   CHAR_BACKWARD_SLASH,
   CHAR_COLON
 } = require('internal/constants');
 
+const asyncESM = require('internal/process/esm_loader');
+const ModuleJob = require('internal/modules/esm/module_job');
+const { ModuleWrap, kInstantiated } = internalBinding('module_wrap');
+const {
+  encodedSepRegEx,
+  packageInternalResolve
+} = require('internal/modules/esm/resolve');
+
 const isWindows = process.platform === 'win32';
 
 const relativeResolveCache = ObjectCreate(null);
@@ -261,6 +269,7 @@ function readPackage(requestPath) {
       name: parsed.name,
       main: parsed.main,
       exports: parsed.exports,
+      imports: parsed.imports,
       type: parsed.type
     };
     packageJsonCache.set(jsonPath, filtered);
@@ -534,21 +543,26 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
     if (subpath.length > 0 && target[target.length - 1] !== '/')
       resolvedTarget = undefined;
     if (resolvedTarget === undefined)
-      throw new ERR_INVALID_PACKAGE_TARGET(StringPrototypeSlice(baseUrl.pathname
-        , 0, -1), mappingKey, subpath, target);
+      throw new ERR_INVALID_PACKAGE_TARGET(baseUrl.pathname, mappingKey,
+                                           target);
     const resolved = new URL(subpath, resolvedTarget);
     const resolvedPath = resolved.pathname;
     if (StringPrototypeStartsWith(resolvedPath, resolvedTargetPath) &&
         StringPrototypeIndexOf(resolvedPath, '/node_modules/',
                                pkgPathPath.length - 1) === -1) {
+      if (StringPrototypeMatch(resolvedPath, encodedSepRegEx))
+        throw new ERR_INVALID_MODULE_SPECIFIER(
+          resolvedPath, 'must not include encoded "/" or "\\" characters',
+          fileURLToPath(baseUrl));
       return fileURLToPath(resolved);
     }
-    throw new ERR_INVALID_MODULE_SPECIFIER(StringPrototypeSlice(baseUrl.pathname
-      , 0, -1), mappingKey);
+    const reason = 'request is not a valid subpath for the "exports" ' +
+      `resolution of ${baseUrl.pathname}package.json`;
+    throw new ERR_INVALID_MODULE_SPECIFIER(mappingKey + subpath, reason);
   } else if (ArrayIsArray(target)) {
     if (target.length === 0)
       throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-        StringPrototypeSlice(baseUrl.pathname, 0, -1), mappingKey + subpath);
+        baseUrl.pathname, mappingKey + subpath);
     let lastException;
     for (const targetValue of target) {
       try {
@@ -590,13 +604,12 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
       }
     }
     throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-      StringPrototypeSlice(baseUrl.pathname, 0, -1), mappingKey + subpath);
+      baseUrl.pathname, mappingKey + subpath);
   } else if (target === null) {
     throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-      StringPrototypeSlice(baseUrl.pathname, 0, -1), mappingKey + subpath);
+      baseUrl.pathname, mappingKey + subpath);
   }
-  throw new ERR_INVALID_PACKAGE_TARGET(
-    StringPrototypeSlice(baseUrl.pathname, 0, -1), mappingKey, subpath, target);
+  throw new ERR_INVALID_PACKAGE_TARGET(baseUrl.pathname, mappingKey, target);
 }
 
 const trailingSlashRegex = /(?:^|\/)\.?\.$/;
@@ -894,6 +907,8 @@ Module._load = function(request, parent, isMain) {
   return module.exports;
 };
 
+// TODO: Use this set when resolving pkg#exports conditions.
+const cjsConditions = new SafeSet(['require', 'node']);
 Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.canBeRequiredByUsers(request)) {
     return request;
@@ -936,6 +951,27 @@ Module._resolveFilename = function(request, parent, isMain, options) {
   }
 
   if (parent && parent.filename) {
+    if (request[0] === '#') {
+      const pkg = readPackageScope(parent.filename) || {};
+      if (pkg.data && pkg.data.imports !== null &&
+          pkg.data.imports !== undefined) {
+        try {
+          const resolved = packageInternalResolve(
+            request, pathToFileURL(parent.filename), cjsConditions);
+          return fileURLToPath(resolved);
+        } catch (err) {
+          if (err.code === 'ERR_MODULE_NOT_FOUND') {
+            // eslint-disable-next-line no-restricted-syntax
+            const err = new Error(`Cannot find module '${request}'`);
+            err.code = 'MODULE_NOT_FOUND';
+            err.path = path.resolve(pkg.path, 'package.json');
+            // TODO(BridgeAR): Add the requireStack as well.
+            throw err;
+          }
+          throw err;
+        }
+      }
+    }
     const filename = trySelf(parent.filename, request);
     if (filename) {
       const cacheKey = request + '\x00' +
@@ -1284,8 +1320,3 @@ Module.syncBuiltinESMExports = function syncBuiltinESMExports() {
 
 // Backwards compatibility
 Module.Module = Module;
-
-// We have to load the esm things after module.exports!
-asyncESM = require('internal/process/esm_loader');
-ModuleJob = require('internal/modules/esm/module_job');
-({ ModuleWrap, kInstantiated } = internalBinding('module_wrap'));
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index 987a139c6aae57..16ca78880c7a15 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -10,6 +10,7 @@ const {
   ObjectGetOwnPropertyNames,
   ObjectPrototypeHasOwnProperty,
   RegExp,
+  RegExpPrototypeTest,
   SafeMap,
   SafeSet,
   String,
@@ -22,7 +23,6 @@ const {
   StringPrototypeStartsWith,
   StringPrototypeSubstr,
 } = primordials;
-const assert = require('internal/assert');
 const internalFS = require('internal/fs/utils');
 const { NativeModule } = require('internal/bootstrap/loaders');
 const {
@@ -44,6 +44,7 @@ const {
   ERR_INVALID_PACKAGE_CONFIG,
   ERR_INVALID_PACKAGE_TARGET,
   ERR_MODULE_NOT_FOUND,
+  ERR_PACKAGE_IMPORT_NOT_DEFINED,
   ERR_PACKAGE_PATH_NOT_EXPORTED,
   ERR_UNSUPPORTED_DIR_IMPORT,
   ERR_UNSUPPORTED_ESM_URL_SCHEME,
@@ -91,11 +92,13 @@ function getPackageConfig(path) {
   const source = packageJsonReader.read(path).string;
   if (source === undefined) {
     const packageConfig = {
+      pjsonPath: path,
       exists: false,
       main: undefined,
       name: undefined,
       type: 'none',
-      exports: undefined
+      exports: undefined,
+      imports: undefined,
     };
     packageJSONCache.set(path, packageConfig);
     return packageConfig;
@@ -109,19 +112,22 @@ function getPackageConfig(path) {
     throw new ERR_INVALID_PACKAGE_CONFIG(errorPath, error.message, true);
   }
 
-  let { main, name, type } = packageJSON;
+  let { imports, main, name, type } = packageJSON;
   const { exports } = packageJSON;
+  if (typeof imports !== 'object' || imports === null) imports = undefined;
   if (typeof main !== 'string') main = undefined;
   if (typeof name !== 'string') name = undefined;
   // Ignore unknown types for forwards compatibility
   if (type !== 'module' && type !== 'commonjs') type = 'none';
 
   const packageConfig = {
+    pjsonPath: path,
     exists: true,
     main,
     name,
     type,
-    exports
+    exports,
+    imports,
   };
   packageJSONCache.set(path, packageConfig);
   return packageConfig;
@@ -143,14 +149,17 @@ function getPackageScopeConfig(resolved, base) {
     // (can't just check "/package.json" for Windows support).
     if (packageJSONUrl.pathname === lastPackageJSONUrl.pathname) break;
   }
+  const packageJSONPath = fileURLToPath(packageJSONUrl);
   const packageConfig = {
+    pjsonPath: packageJSONPath,
     exists: false,
     main: undefined,
     name: undefined,
     type: 'none',
-    exports: undefined
+    exports: undefined,
+    imports: undefined,
   };
-  packageJSONCache.set(fileURLToPath(packageJSONUrl), packageConfig);
+  packageJSONCache.set(packageJSONPath, packageConfig);
   return packageConfig;
 }
 
@@ -233,6 +242,7 @@ function resolveIndex(search) {
   return resolveExtensions(new URL('index', search));
 }
 
+const encodedSepRegEx = /%2F|%2C/i;
 function finalizeResolution(resolved, base) {
   if (getOptionValue('--experimental-specifier-resolution') === 'node') {
     let file = resolveExtensionsWithTryExactName(resolved);
@@ -247,6 +257,11 @@ function finalizeResolution(resolved, base) {
       resolved.pathname, fileURLToPath(base), 'module');
   }
 
+  if (RegExpPrototypeTest(encodedSepRegEx, resolved.pathname))
+    throw new ERR_INVALID_MODULE_SPECIFIER(
+      resolved.pathname, 'must not include encoded "/" or "\\" characters',
+      fileURLToPath(base));
+
   const path = fileURLToPath(resolved);
   const stats = tryStatSync(path);
 
@@ -263,34 +278,52 @@ function finalizeResolution(resolved, base) {
   return resolved;
 }
 
+function throwImportNotDefined(specifier, packageJSONUrl, base) {
+  throw new ERR_PACKAGE_IMPORT_NOT_DEFINED(
+    specifier, packageJSONUrl && fileURLToPath(new URL('.', packageJSONUrl)),
+    fileURLToPath(base));
+}
+
 function throwExportsNotFound(subpath, packageJSONUrl, base) {
   throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-    fileURLToPath(packageJSONUrl), subpath, fileURLToPath(base));
+    fileURLToPath(new URL('.', packageJSONUrl)), subpath, fileURLToPath(base));
 }
 
-function throwSubpathInvalid(subpath, packageJSONUrl, base) {
-  throw new ERR_INVALID_MODULE_SPECIFIER(
-    fileURLToPath(packageJSONUrl), subpath, fileURLToPath(base));
+function throwInvalidSubpath(subpath, packageJSONUrl, internal, base) {
+  const reason = `request is not a valid subpath for the "${internal ?
+    'imports' : 'exports'}" resolution of ${fileURLToPath(packageJSONUrl)}${
+    base ? ` imported from ${base}` : ''}`;
+  throw new ERR_INVALID_MODULE_SPECIFIER(subpath, reason, fileURLToPath(base));
 }
 
-function throwExportsInvalid(
-  subpath, target, packageJSONUrl, base) {
+function throwInvalidPackageTarget(
+  subpath, target, packageJSONUrl, internal, base) {
   if (typeof target === 'object' && target !== null) {
     target = JSONStringify(target, null, '');
-  } else if (ArrayIsArray(target)) {
-    target = `[${target}]`;
   } else {
     target = `${target}`;
   }
   throw new ERR_INVALID_PACKAGE_TARGET(
-    fileURLToPath(packageJSONUrl), null, subpath, target, fileURLToPath(base));
+    fileURLToPath(new URL('.', packageJSONUrl)), subpath, target,
+    internal, fileURLToPath(base));
 }
 
-function resolveExportsTargetString(
-  target, subpath, match, packageJSONUrl, base) {
-  if (target[0] !== '.' || target[1] !== '/' ||
-      (subpath !== '' && target[target.length - 1] !== '/')) {
-    throwExportsInvalid(match, target, packageJSONUrl, base);
+function resolvePackageTargetString(
+  target, subpath, match, packageJSONUrl, base, internal, conditions) {
+  if (subpath !== '' && target[target.length - 1] !== '/')
+    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);
+
+  if (!target.startsWith('./')) {
+    if (internal && !target.startsWith('../') && !target.startsWith('/')) {
+      let isURL = false;
+      try {
+        new URL(target);
+        isURL = true;
+      } catch {}
+      if (!isURL)
+        return packageResolve(target + subpath, base, conditions);
+    }
+    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);
   }
 
   const resolved = new URL(target, packageJSONUrl);
@@ -299,18 +332,16 @@ function resolveExportsTargetString(
 
   if (!StringPrototypeStartsWith(resolvedPath, packagePath) ||
       StringPrototypeIncludes(
-        resolvedPath, '/node_modules/', packagePath.length - 1)) {
-    throwExportsInvalid(match, target, packageJSONUrl, base);
-  }
+        resolvedPath, '/node_modules/', packagePath.length - 1))
+    throwInvalidPackageTarget(match, target, packageJSONUrl, internal, base);
 
   if (subpath === '') return resolved;
   const subpathResolved = new URL(subpath, resolved);
   const subpathResolvedPath = subpathResolved.pathname;
   if (!StringPrototypeStartsWith(subpathResolvedPath, resolvedPath) ||
       StringPrototypeIncludes(subpathResolvedPath,
-                              '/node_modules/', packagePath.length - 1)) {
-    throwSubpathInvalid(match + subpath, packageJSONUrl, base);
-  }
+                              '/node_modules/', packagePath.length - 1))
+    throwInvalidSubpath(match + subpath, packageJSONUrl, internal, base);
   return subpathResolved;
 }
 
@@ -324,36 +355,43 @@ function isArrayIndex(key) {
   return keyNum >= 0 && keyNum < 0xFFFF_FFFF;
 }
 
-function resolveExportsTarget(
-  packageJSONUrl, target, subpath, packageSubpath, base, conditions) {
+function resolvePackageTarget(
+  packageJSONUrl, target, subpath, packageSubpath, base, internal, conditions) {
   if (typeof target === 'string') {
-    const resolved = resolveExportsTargetString(
-      target, subpath, packageSubpath, packageJSONUrl, base);
+    const resolved = resolvePackageTargetString(
+      target, subpath, packageSubpath, packageJSONUrl, base, internal,
+      conditions);
+    if (resolved === null)
+      return null;
     return finalizeResolution(resolved, base);
   } else if (ArrayIsArray(target)) {
     if (target.length === 0)
-      throwExportsNotFound(packageSubpath, packageJSONUrl, base);
+      return null;
 
     let lastException;
     for (let i = 0; i < target.length; i++) {
       const targetItem = target[i];
       let resolved;
       try {
-        resolved = resolveExportsTarget(
-          packageJSONUrl, targetItem, subpath, packageSubpath, base,
+        resolved = resolvePackageTarget(
+          packageJSONUrl, targetItem, subpath, packageSubpath, base, internal,
           conditions);
       } catch (e) {
         lastException = e;
-        if (e.code === 'ERR_PACKAGE_PATH_NOT_EXPORTED' ||
-            e.code === 'ERR_INVALID_PACKAGE_TARGET') {
+        if (e.code === 'ERR_INVALID_PACKAGE_TARGET')
           continue;
-        }
         throw e;
       }
-
+      if (resolved === undefined)
+        continue;
+      if (resolved === null) {
+        lastException = null;
+        continue;
+      }
       return finalizeResolution(resolved, base);
     }
-    assert(lastException !== undefined);
+    if (lastException === undefined || lastException === null)
+      return lastException;
     throw lastException;
   } else if (typeof target === 'object' && target !== null) {
     const keys = ObjectGetOwnPropertyNames(target);
@@ -369,21 +407,20 @@ function resolveExportsTarget(
       const key = keys[i];
       if (key === 'default' || conditions.has(key)) {
         const conditionalTarget = target[key];
-        try {
-          return resolveExportsTarget(
-            packageJSONUrl, conditionalTarget, subpath, packageSubpath, base,
-            conditions);
-        } catch (e) {
-          if (e.code === 'ERR_PACKAGE_PATH_NOT_EXPORTED') continue;
-          throw e;
-        }
+        const resolved = resolvePackageTarget(
+          packageJSONUrl, conditionalTarget, subpath, packageSubpath, base,
+          internal, conditions);
+        if (resolved === undefined)
+          continue;
+        return resolved;
       }
     }
-    throwExportsNotFound(packageSubpath, packageJSONUrl, base);
+    return undefined;
   } else if (target === null) {
-    throwExportsNotFound(packageSubpath, packageJSONUrl, base);
+    return null;
   }
-  throwExportsInvalid(packageSubpath, target, packageJSONUrl, base);
+  throwInvalidPackageTarget(packageSubpath, target, packageJSONUrl, internal,
+                            base);
 }
 
 function isConditionalExportsMainSugar(exports, packageJSONUrl, base) {
@@ -409,19 +446,25 @@ function isConditionalExportsMainSugar(exports, packageJSONUrl, base) {
   return isConditionalSugar;
 }
 
-
 function packageMainResolve(packageJSONUrl, packageConfig, base, conditions) {
   if (packageConfig.exists) {
     const exports = packageConfig.exports;
     if (exports !== undefined) {
       if (isConditionalExportsMainSugar(exports, packageJSONUrl, base)) {
-        return resolveExportsTarget(packageJSONUrl, exports, '', '', base,
-                                    conditions);
+        const resolved = resolvePackageTarget(packageJSONUrl, exports, '', '',
+                                              base, false, conditions);
+        if (resolved === null || resolved === undefined)
+          throwExportsNotFound('.', packageJSONUrl, base);
+        return resolved;
       } else if (typeof exports === 'object' && exports !== null) {
         const target = exports['.'];
-        if (target !== undefined)
-          return resolveExportsTarget(packageJSONUrl, target, '', '', base,
-                                      conditions);
+        if (target !== undefined) {
+          const resolved = resolvePackageTarget(packageJSONUrl, target, '', '',
+                                                base, false, conditions);
+          if (resolved === null || resolved === undefined)
+            throwExportsNotFound('.', packageJSONUrl, base);
+          return resolved;
+        }
       }
 
       throw new ERR_PACKAGE_PATH_NOT_EXPORTED(packageJSONUrl, '.');
@@ -457,11 +500,12 @@ function packageExportsResolve(
     throwExportsNotFound(packageSubpath, packageJSONUrl, base);
   }
 
-
   if (ObjectPrototypeHasOwnProperty(exports, packageSubpath)) {
     const target = exports[packageSubpath];
-    const resolved = resolveExportsTarget(
-      packageJSONUrl, target, '', packageSubpath, base, conditions);
+    const resolved = resolvePackageTarget(
+      packageJSONUrl, target, '', packageSubpath, base, false, conditions);
+    if (resolved === null || resolved === undefined)
+      throwExportsNotFound(packageSubpath, packageJSONUrl, base);
     return finalizeResolution(resolved, base);
   }
 
@@ -479,14 +523,59 @@ function packageExportsResolve(
   if (bestMatch) {
     const target = exports[bestMatch];
     const subpath = StringPrototypeSubstr(packageSubpath, bestMatch.length);
-    const resolved = resolveExportsTarget(
-      packageJSONUrl, target, subpath, packageSubpath, base, conditions);
+    const resolved = resolvePackageTarget(
+      packageJSONUrl, target, subpath, bestMatch, base, false, conditions);
+    if (resolved === null || resolved === undefined)
+      throwExportsNotFound(packageSubpath, packageJSONUrl, base);
     return finalizeResolution(resolved, base);
   }
 
   throwExportsNotFound(packageSubpath, packageJSONUrl, base);
 }
 
+function packageInternalResolve(name, base, conditions) {
+  if (name === '#' || name.startsWith('#/')) {
+    const reason = 'is not a valid internal imports specifier name';
+    throw new ERR_INVALID_MODULE_SPECIFIER(name, reason, fileURLToPath(base));
+  }
+  let packageJSONUrl;
+  const packageConfig = getPackageScopeConfig(base, base);
+  if (packageConfig.exists) {
+    packageJSONUrl = pathToFileURL(packageConfig.pjsonPath);
+    const imports = packageConfig.imports;
+    if (imports) {
+      if (ObjectPrototypeHasOwnProperty(imports, name)) {
+        const resolved = resolvePackageTarget(
+          packageJSONUrl, imports[name], '', name, base, true, conditions);
+        if (resolved !== null)
+          return finalizeResolution(resolved, base);
+      } else {
+        let bestMatch = '';
+        const keys = ObjectGetOwnPropertyNames(imports);
+        for (let i = 0; i < keys.length; i++) {
+          const key = keys[i];
+          if (key[key.length - 1] !== '/') continue;
+          if (StringPrototypeStartsWith(name, key) &&
+              key.length > bestMatch.length) {
+            bestMatch = key;
+          }
+        }
+
+        if (bestMatch) {
+          const target = imports[bestMatch];
+          const subpath = StringPrototypeSubstr(name, bestMatch.length);
+          const resolved = resolvePackageTarget(
+            packageJSONUrl, target, subpath, bestMatch, base, true,
+            conditions);
+          if (resolved !== null)
+            return finalizeResolution(resolved, base);
+        }
+      }
+    }
+  }
+  throwImportNotDefined(name, packageJSONUrl, base);
+}
+
 function getPackageType(url) {
   const packageConfig = getPackageScopeConfig(url, url);
   return packageConfig.type;
@@ -526,7 +615,7 @@ function packageResolve(specifier, base, conditions) {
 
   if (!validPackageName) {
     throw new ERR_INVALID_MODULE_SPECIFIER(
-      specifier, undefined, fileURLToPath(base));
+      specifier, 'is not a valid package name', fileURLToPath(base));
   }
 
   const packageSubpath = separatorIndex === -1 ?
@@ -535,17 +624,8 @@ function packageResolve(specifier, base, conditions) {
   // ResolveSelf
   const packageConfig = getPackageScopeConfig(base, base);
   if (packageConfig.exists) {
-    // TODO(jkrems): Find a way to forward the pair/iterator already generated
-    // while executing GetPackageScopeConfig
-    let packageJSONUrl;
-    for (const [ filename, packageConfigCandidate ] of packageJSONCache) {
-      if (packageConfig === packageConfigCandidate) {
-        packageJSONUrl = pathToFileURL(filename);
-        break;
-      }
-    }
-    if (packageJSONUrl !== undefined &&
-        packageConfig.name === packageName &&
+    const packageJSONUrl = pathToFileURL(packageConfig.pjsonPath);
+    if (packageConfig.name === packageName &&
         packageConfig.exports !== undefined) {
       if (packageSubpath === './') {
         return new URL('./', packageJSONUrl);
@@ -626,6 +706,8 @@ function moduleResolve(specifier, base, conditions) {
   let resolved;
   if (shouldBeTreatedAsRelativeOrAbsolutePath(specifier)) {
     resolved = new URL(specifier, base);
+  } else if (specifier[0] === '#') {
+    resolved = packageInternalResolve(specifier, base, conditions);
   } else {
     try {
       resolved = new URL(specifier);
@@ -764,5 +846,7 @@ function defaultResolve(specifier, context = {}, defaultResolveUnused) {
 module.exports = {
   DEFAULT_CONDITIONS,
   defaultResolve,
-  getPackageType
+  encodedSepRegEx,
+  getPackageType,
+  packageInternalResolve
 };
diff --git a/src/node_file.cc b/src/node_file.cc
index 83b3f2f6d00a57..968cf6f27c4f74 100644
--- a/src/node_file.cc
+++ b/src/node_file.cc
@@ -946,6 +946,7 @@ static void InternalModuleReadJSON(const FunctionCallbackInfo<Value>& args) {
       if (0 == memcmp(s, "type", 4)) break;
     } else if (n == 7) {
       if (0 == memcmp(s, "exports", 7)) break;
+      if (0 == memcmp(s, "imports", 7)) break;
     }
   }
 
diff --git a/test/es-module/test-esm-exports.mjs b/test/es-module/test-esm-exports.mjs
index a0348d4a1ab0b2..02caceee64deaa 100644
--- a/test/es-module/test-esm-exports.mjs
+++ b/test/es-module/test-esm-exports.mjs
@@ -118,7 +118,8 @@ import fromInside from '../fixtures/node_modules/pkgexports/lib/hole.js';
   for (const [specifier, subpath] of invalidSpecifiers) {
     loadFixture(specifier).catch(mustCall((err) => {
       strictEqual(err.code, 'ERR_INVALID_MODULE_SPECIFIER');
-      assertStartsWith(err.message, 'Package subpath ');
+      assertStartsWith(err.message, 'Invalid module ');
+      assertIncludes(err.message, 'is not a valid subpath');
       assertIncludes(err.message, subpath);
     }));
   }
@@ -161,7 +162,7 @@ import fromInside from '../fixtures/node_modules/pkgexports/lib/hole.js';
 
   // The use of %2F escapes in paths fails loading
   loadFixture('pkgexports/sub/..%2F..%2Fbar.js').catch(mustCall((err) => {
-    strictEqual(err.code, 'ERR_INVALID_FILE_URL_PATH');
+    strictEqual(err.code, 'ERR_INVALID_MODULE_SPECIFIER');
   }));
 
   // Package export with numeric index properties must throw a validation error
diff --git a/test/es-module/test-esm-imports.mjs b/test/es-module/test-esm-imports.mjs
new file mode 100644
index 00000000000000..694496a2ff2c93
--- /dev/null
+++ b/test/es-module/test-esm-imports.mjs
@@ -0,0 +1,117 @@
+import { mustCall } from '../common/index.mjs';
+import { ok, deepStrictEqual, strictEqual } from 'assert';
+
+import importer from '../fixtures/es-modules/pkgimports/importer.js';
+import { requireFixture } from '../fixtures/pkgexports.mjs';
+
+const { requireImport, importImport } = importer;
+
+[requireImport, importImport].forEach((loadFixture) => {
+  const isRequire = loadFixture === requireImport;
+
+  const internalImports = new Map([
+    // Base case
+    ['#test', { default: 'test' }],
+    // import / require conditions
+    ['#branch', { default: isRequire ? 'requirebranch' : 'importbranch' }],
+    // Subpath imports
+    ['#subpath/x.js', { default: 'xsubpath' }],
+    // External imports
+    ['#external', { default: 'asdf' }],
+    // External subpath imports
+    ['#external/subpath/asdf.js', { default: 'asdf' }],
+  ]);
+
+  for (const [validSpecifier, expected] of internalImports) {
+    if (validSpecifier === null) continue;
+
+    loadFixture(validSpecifier)
+      .then(mustCall((actual) => {
+        deepStrictEqual({ ...actual }, expected);
+      }));
+  }
+
+  const invalidImportTargets = new Set([
+    // External subpath import without trailing slash
+    ['#external/invalidsubpath/x', '#external/invalidsubpath/'],
+    // Target steps below the package base
+    ['#belowbase', '#belowbase'],
+    // Target is a URL
+    ['#url', '#url'],
+  ]);
+
+  for (const [specifier, subpath] of invalidImportTargets) {
+    loadFixture(specifier).catch(mustCall((err) => {
+      strictEqual(err.code, 'ERR_INVALID_PACKAGE_TARGET');
+      assertStartsWith(err.message, 'Invalid "imports"');
+      assertIncludes(err.message, subpath);
+      assertNotIncludes(err.message, 'targets must start with');
+    }));
+  }
+
+  const invalidImportSpecifiers = new Map([
+    // Backtracking below the package base
+    ['#subpath/sub/../../../belowbase', 'request is not a valid subpath'],
+    // Percent-encoded slash errors
+    ['#external/subpath/x%2Fy', 'must not include encoded "/"'],
+    // Target must have a name
+    ['#', '#'],
+    // Initial slash target must have a leading name
+    ['#/initialslash', '#/initialslash'],
+    // Percent-encoded target paths
+    ['#percent', 'must not include encoded "/"'],
+  ]);
+
+  for (const [specifier, expected] of invalidImportSpecifiers) {
+    loadFixture(specifier).catch(mustCall((err) => {
+      strictEqual(err.code, 'ERR_INVALID_MODULE_SPECIFIER');
+      assertStartsWith(err.message, 'Invalid module');
+      assertIncludes(err.message, expected);
+    }));
+  }
+
+  const undefinedImports = new Set([
+    // Missing import
+    '#missing',
+    // Explicit null import
+    '#null',
+    // No condition match import
+    '#nullcondition',
+    // Null subpath shadowing
+    '#subpath/nullshadow/x',
+  ]);
+
+  for (const specifier of undefinedImports) {
+    loadFixture(specifier).catch(mustCall((err) => {
+      strictEqual(err.code, 'ERR_PACKAGE_IMPORT_NOT_DEFINED');
+      assertStartsWith(err.message, 'Package import ');
+      assertIncludes(err.message, specifier);
+    }));
+  }
+
+  // Handle not found for the defined imports target not existing
+  loadFixture('#notfound').catch(mustCall((err) => {
+    strictEqual(err.code,
+                isRequire ? 'MODULE_NOT_FOUND' : 'ERR_MODULE_NOT_FOUND');
+  }));
+});
+
+// CJS resolver must still support #package packages in node_modules
+requireFixture('#cjs').then(mustCall((actual) => {
+  strictEqual(actual.default, 'cjs backcompat');
+}));
+
+function assertStartsWith(actual, expected) {
+  const start = actual.toString().substr(0, expected.length);
+  strictEqual(start, expected);
+}
+
+function assertIncludes(actual, expected) {
+  ok(actual.toString().indexOf(expected) !== -1,
+     `${JSON.stringify(actual)} includes ${JSON.stringify(expected)}`);
+}
+
+function assertNotIncludes(actual, expected) {
+  ok(actual.toString().indexOf(expected) === -1,
+     `${JSON.stringify(actual)} doesn't include ${JSON.stringify(expected)}`);
+}
diff --git a/test/fixtures/es-modules/pkgimports/importbranch.js b/test/fixtures/es-modules/pkgimports/importbranch.js
new file mode 100644
index 00000000000000..ebae53309112a8
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/importbranch.js
@@ -0,0 +1,2 @@
+module.exports = 'importbranch';
+
diff --git a/test/fixtures/es-modules/pkgimports/importer.js b/test/fixtures/es-modules/pkgimports/importer.js
new file mode 100644
index 00000000000000..30fe06bd613492
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/importer.js
@@ -0,0 +1,4 @@
+module.exports = {
+  importImport: x => import(x),
+  requireImport: x => Promise.resolve(x).then(x => ({ default: require(x) }))
+};
diff --git a/test/fixtures/es-modules/pkgimports/package.json b/test/fixtures/es-modules/pkgimports/package.json
new file mode 100644
index 00000000000000..7cd179631fa618
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/package.json
@@ -0,0 +1,30 @@
+{
+  "imports": {
+    "#test": "./test.js",
+    "#branch": {
+      "import": "./importbranch.js",
+      "require": "./requirebranch.js"
+    },
+    "#subpath/": "./sub/",
+    "#external": "pkgexports/valid-cjs",
+    "#external/subpath/": "pkgexports/sub/",
+    "#external/invalidsubpath/": "pkgexports/sub",
+    "#belowbase": "../belowbase",
+    "#url": "some:url",
+    "#null": null,
+    "#nullcondition": {
+      "import": {
+        "default": null
+      },
+      "require": {
+        "default": null
+      },
+      "default": "./test.js"
+    },
+    "#subpath/nullshadow/": [null],
+    "#": "./test.js",
+    "#/initialslash": "./test.js",
+    "#notfound": "./notfound.js",
+    "#percent": "./..%2F/x.js"
+  }
+}
diff --git a/test/fixtures/es-modules/pkgimports/requirebranch.js b/test/fixtures/es-modules/pkgimports/requirebranch.js
new file mode 100644
index 00000000000000..fd58e34be95332
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/requirebranch.js
@@ -0,0 +1,2 @@
+module.exports = 'requirebranch';
+
diff --git a/test/fixtures/es-modules/pkgimports/sub/x.js b/test/fixtures/es-modules/pkgimports/sub/x.js
new file mode 100644
index 00000000000000..48cca8c5646659
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/sub/x.js
@@ -0,0 +1,2 @@
+module.exports = 'xsubpath';
+
diff --git a/test/fixtures/es-modules/pkgimports/test.js b/test/fixtures/es-modules/pkgimports/test.js
new file mode 100644
index 00000000000000..37a4648424da6a
--- /dev/null
+++ b/test/fixtures/es-modules/pkgimports/test.js
@@ -0,0 +1 @@
+module.exports = 'test';
diff --git a/test/fixtures/node_modules/#cjs/index.js b/test/fixtures/node_modules/#cjs/index.js
new file mode 100644
index 00000000000000..c60af759886ce6
--- /dev/null
+++ b/test/fixtures/node_modules/#cjs/index.js
@@ -0,0 +1,2 @@
+module.exports = 'cjs backcompat';
+