diff --git a/docs/rules/0128/resource-reconciling-field.md b/docs/rules/0128/resource-reconciling-field.md
new file mode 100644
index 000000000..f766e2cc1
--- /dev/null
+++ b/docs/rules/0128/resource-reconciling-field.md
@@ -0,0 +1,95 @@
+---
+rule:
+  aip: 128
+  name: [core, '0128', resource-reconciling-field]
+  summary: Declarative-friendly resources must have a `reconciling` field.
+permalink: /128/resource-reconciling-field
+redirect_from:
+  - /0128/resource-reconciling-field
+---
+
+# Declarative-friendly resources: Reconciling field
+
+This rule enforces that all declarative-friendly resources have a `bool
+reconciling` field, as mandated in [AIP-128][].
+
+## Details
+
+This rule looks at any message with a `google.api.resource` annotation that
+includes `style: DECLARATIVE_FRIENDLY`, and complains if the `reconciling` field
+is missing or if it has any type other than `bool`.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+// The `reconciling` field is missing.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+    style: DECLARATIVE_FRIENDLY
+  };
+
+  string name = 1;
+}
+```
+
+```proto
+// Incorrect.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+    style: DECLARATIVE_FRIENDLY
+  };
+
+  string name = 1;
+  int32 reconciling = 2; // Type should be `bool`.
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+    style: DECLARATIVE_FRIENDLY
+  };
+
+  string name = 1;
+  bool reconciling = 2;
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the message (if
+the `reconciling` field is missing) or above the field (if it is the wrong
+type). Remember to also include an [aip.dev/not-precedent][] comment explaining
+why.
+
+```proto
+// (-- api-linter: core::0128::resource-reconciling-field=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+    style: DECLARATIVE_FRIENDLY
+  };
+
+  string name = 1;
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-128]: https://aip.dev/128
+[aip.dev/not-precedent]: https://aip.dev/not-precedent
diff --git a/rules/aip0128/aip0128.go b/rules/aip0128/aip0128.go
index 27f96e0bc..6dd615b82 100644
--- a/rules/aip0128/aip0128.go
+++ b/rules/aip0128/aip0128.go
@@ -25,5 +25,6 @@ func AddRules(r lint.RuleRegistry) error {
 	return r.Register(
 		128,
 		resourceAnnotationsField,
+		resourceReconcilingField,
 	)
 }
diff --git a/rules/aip0128/resource_reconciling_field.go b/rules/aip0128/resource_reconciling_field.go
new file mode 100644
index 000000000..abc06650a
--- /dev/null
+++ b/rules/aip0128/resource_reconciling_field.go
@@ -0,0 +1,55 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0128
+
+import (
+	"fmt"
+
+	"github.com/googleapis/api-linter/lint"
+	"github.com/googleapis/api-linter/locations"
+	"github.com/googleapis/api-linter/rules/internal/utils"
+	"github.com/jhump/protoreflect/desc"
+	"github.com/jhump/protoreflect/desc/builder"
+)
+
+var resourceReconcilingField = &lint.MessageRule{
+	Name: lint.NewRuleName(128, "resource-reconciling-field"),
+	OnlyIf: func(m *desc.MessageDescriptor) bool {
+		// IsDeclarativeFriendly returns true for both
+		// resources and request messages, but we only care about resources.
+		resource := utils.DeclarativeFriendlyResource(m)
+		return resource != nil && resource == m
+	},
+	LintMessage: func(m *desc.MessageDescriptor) []lint.Problem {
+		f := m.FindFieldByName("reconciling")
+		if f == nil {
+			return []lint.Problem{{
+				Message:    fmt.Sprintf("Declarative-friendly %q has no `reconciling` field.", m.GetName()),
+				Descriptor: m,
+			}}
+		}
+
+		if f.GetType() != builder.FieldTypeBool().GetType() || f.IsRepeated() {
+			return []lint.Problem{{
+				Message:    "The `reconciling` field should be a singular bool.",
+				Descriptor: f,
+				Location:   locations.FieldType(f),
+				Suggestion: "bool",
+			}}
+		}
+
+		return nil
+	},
+}
diff --git a/rules/aip0128/resource_reconciling_field_test.go b/rules/aip0128/resource_reconciling_field_test.go
new file mode 100644
index 000000000..5f3832276
--- /dev/null
+++ b/rules/aip0128/resource_reconciling_field_test.go
@@ -0,0 +1,61 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0128
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+	"github.com/jhump/protoreflect/desc"
+)
+
+func TestResourceReconcilingField(t *testing.T) {
+	for _, test := range []struct {
+		name        string
+		Style       string
+		Reconciling string
+		problems    testutils.Problems
+	}{
+		{"ValidMissingNotDF", "", "", nil},
+		{"ValidPresentNotDF", "", "bool reconciling = 2;", nil},
+		{"ValidBadTypeNotDF", "", "int32 reconciling = 2;", nil},
+		{"ValidPresentDF", "style: DECLARATIVE_FRIENDLY", "bool reconciling = 2;", nil},
+		{"InvalidMissingDF", "style: DECLARATIVE_FRIENDLY", "", testutils.Problems{{Message: "reconciling"}}},
+		{"InvalidBadTypeDF", "style: DECLARATIVE_FRIENDLY", "int32 reconciling = 2;", testutils.Problems{{Suggestion: "bool"}}},
+		{"InvalidRepeatedDF", "style: DECLARATIVE_FRIENDLY", "repeated bool reconciling = 2;", testutils.Problems{{Suggestion: "bool"}}},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+				import "google/api/resource.proto";
+				message Book {
+					option (google.api.resource) = {
+						type: "library.googleapis.com/Book"
+						{{.Style}}
+					};
+					string name = 1;
+					{{.Reconciling}}
+				}
+				message DeleteBookRequest {}
+			`, test)
+			var d desc.Descriptor = f.GetMessageTypes()[0]
+			if test.name == "InvalidBadTypeDF" || test.name == "InvalidRepeatedDF" {
+				d = f.GetMessageTypes()[0].GetFields()[1]
+			}
+			if diff := test.problems.SetDescriptor(d).Diff(resourceReconcilingField.Lint(f)); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}