diff --git a/.changes/unreleased/Fixes-20240715-205355.yaml b/.changes/unreleased/Fixes-20240715-205355.yaml
new file mode 100644
index 00000000..780a6ad9
--- /dev/null
+++ b/.changes/unreleased/Fixes-20240715-205355.yaml
@@ -0,0 +1,6 @@
+kind: Fixes
+body: Fix case-insensitive env vars for Windows
+time: 2024-07-15T20:53:55.946355+01:00
+custom:
+    Author: peterallenwebb aranke
+    Issue: "166"
diff --git a/dbt_common/context.py b/dbt_common/context.py
index d1775c55..947d409a 100644
--- a/dbt_common/context.py
+++ b/dbt_common/context.py
@@ -1,15 +1,46 @@
+import os
 from contextvars import ContextVar, copy_context
-from typing import List, Mapping, Optional
+from typing import List, Mapping, Optional, Iterator
 
 from dbt_common.constants import PRIVATE_ENV_PREFIX, SECRET_ENV_PREFIX
 from dbt_common.record import Recorder
 
 
+class CaseInsensitiveMapping(Mapping):
+    def __init__(self, env: Mapping[str, str]):
+        self._env = {k.casefold(): (k, v) for k, v in env.items()}
+
+    def __getitem__(self, key: str) -> str:
+        return self._env[key.casefold()][1]
+
+    def __len__(self) -> int:
+        return len(self._env)
+
+    def __iter__(self) -> Iterator[str]:
+        for item in self._env.items():
+            yield item[0]
+
+
 class InvocationContext:
     def __init__(self, env: Mapping[str, str]):
-        self._env = {k: v for k, v in env.items() if not k.startswith(PRIVATE_ENV_PREFIX)}
+        self._env: Mapping[str, str]
+
+        env_public = {}
+        env_private = {}
+
+        for k, v in env.items():
+            if k.startswith(PRIVATE_ENV_PREFIX):
+                env_private[k] = v
+            else:
+                env_public[k] = v
+
+        if os.name == "nt":
+            self._env = CaseInsensitiveMapping(env_public)
+        else:
+            self._env = env_public
+
         self._env_secrets: Optional[List[str]] = None
-        self._env_private = {k: v for k, v in env.items() if k.startswith(PRIVATE_ENV_PREFIX)}
+        self._env_private = env_private
         self.recorder: Optional[Recorder] = None
         # This class will also eventually manage the invocation_id, flags, event manager, etc.
 
diff --git a/pyproject.toml b/pyproject.toml
index 64fc04fc..ba306437 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -126,6 +126,7 @@ ignore = ["E203", "E501", "E741", "W503", "W504"]
 exclude = [
     "dbt_common/events/types_pb2.py",
     "venv",
+    ".venv",
     "env*"
 ]
 per-file-ignores = ["*/__init__.py: F401"]
diff --git a/tests/unit/test_invocation_context.py b/tests/unit/test_invocation_context.py
index 3dc832d3..fbf060ba 100644
--- a/tests/unit/test_invocation_context.py
+++ b/tests/unit/test_invocation_context.py
@@ -1,5 +1,9 @@
+import os
+
+import pytest
+
 from dbt_common.constants import PRIVATE_ENV_PREFIX, SECRET_ENV_PREFIX
-from dbt_common.context import InvocationContext
+from dbt_common.context import InvocationContext, CaseInsensitiveMapping
 
 
 def test_invocation_context_env() -> None:
@@ -8,6 +12,17 @@ def test_invocation_context_env() -> None:
     assert ic.env == test_env
 
 
+@pytest.mark.skipif(
+    os.name != "nt", reason="Test for case-insensitive env vars, only run on Windows"
+)
+def test_invocation_context_windows() -> None:
+    test_env = {"var_1": "lowercase", "vAr_2": "mixedcase", "VAR_3": "uppercase"}
+    ic = InvocationContext(env=test_env)
+    assert ic.env == CaseInsensitiveMapping(
+        {"var_1": "lowercase", "var_2": "mixedcase", "var_3": "uppercase"}
+    )
+
+
 def test_invocation_context_secrets() -> None:
     test_env = {
         f"{SECRET_ENV_PREFIX}_VAR_1": "secret1",