diff --git a/internal/resources/extension/delete.go b/internal/resources/extension/delete.go
new file mode 100644
index 0000000..d239d3d
--- /dev/null
+++ b/internal/resources/extension/delete.go
@@ -0,0 +1,69 @@
+package extension
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/hashicorp/terraform-plugin-framework/diag"
+	"github.com/hashicorp/terraform-plugin-framework/path"
+	kernel "github.com/kernel/kernel-go-sdk"
+	"github.com/kernel/terraform-provider-kernel/internal/projectscope"
+)
+
+type extensionDeleter interface {
+	DeleteExtension(context.Context, string, string) error
+}
+
+func deleteExtension(ctx context.Context, client extensionDeleter, state extensionModel) diag.Diagnostics {
+	var diags diag.Diagnostics
+	if client == nil {
+		diags.AddError("Missing Kernel Client", "The Kernel provider was not configured before using the extension resource.")
+		return diags
+	}
+
+	id, ok := extensionStateID(state, "delete", &diags)
+	if !ok {
+		return diags
+	}
+	if state.ProjectID.IsUnknown() {
+		diags.AddAttributeError(path.Root("project_id"), "Unknown Kernel Project ID", "Cannot delete a Kernel extension while project_id is unknown in Terraform state.")
+		return diags
+	}
+
+	projectID := state.ProjectID.ValueString()
+	if err := client.DeleteExtension(ctx, projectID, id); err != nil {
+		if projectscope.IsNotFound(err) {
+			return diags
+		}
+		if extensionDeleteInUse(err) {
+			diags.AddError(
+				"Delete Kernel Extension",
+				fmt.Sprintf("Kernel refused to delete extension %q because one or more browser pools reference it. Remove the extension from those durable browser pool configurations, then retry. Terraform will not mutate browser pools or running browsers implicitly.", id),
+			)
+			return diags
+		}
+		projectscope.AddError(&diags, "Delete Kernel Extension", projectID, fmt.Errorf("delete extension %q: %w", id, err))
+	}
+	return diags
+}
+
+func extensionDeleteInUse(err error) bool {
+	var apiError *kernel.Error
+	if !errors.As(err, &apiError) || apiError.StatusCode != http.StatusBadRequest {
+		return false
+	}
+
+	var body struct {
+		Code  string `json:"code"`
+		Error struct {
+			Code string `json:"code"`
+		} `json:"error"`
+	}
+	if json.Unmarshal([]byte(apiError.RawJSON()), &body) != nil {
+		return false
+	}
+	return body.Code == "resource_in_use" || body.Error.Code == "resource_in_use"
+}
diff --git a/internal/resources/extension/delete_test.go b/internal/resources/extension/delete_test.go
new file mode 100644
index 0000000..2710097
--- /dev/null
+++ b/internal/resources/extension/delete_test.go
@@ -0,0 +1,112 @@
+package extension
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-framework/types"
+	"github.com/kernel/terraform-provider-kernel/internal/kernelclient"
+)
+
+var _ extensionDeleter = kernelclient.Clients{}
+
+type fakeExtensionDeleter struct {
+	delete func(context.Context, string, string) error
+}
+
+func (f fakeExtensionDeleter) DeleteExtension(ctx context.Context, projectID, id string) error {
+	if f.delete == nil {
+		return errors.New("unexpected delete")
+	}
+	return f.delete(ctx, projectID, id)
+}
+
+func TestDeleteExtensionUsesStateIdentityAndScope(t *testing.T) {
+	t.Parallel()
+
+	var gotProjectID, gotID string
+	diags := deleteExtension(context.Background(), fakeExtensionDeleter{
+		delete: func(ctx context.Context, projectID, id string) error {
+			gotProjectID, gotID = projectID, id
+			return nil
+		},
+	}, extensionModel{ID: types.StringValue("extension_123"), ProjectID: types.StringValue("project_123")})
+	if diags.HasError() {
+		t.Fatalf("unexpected diagnostics: %v", diags)
+	}
+	if gotProjectID != "project_123" || gotID != "extension_123" {
+		t.Fatalf("DeleteExtension scope/id = %q/%q, want project_123/extension_123", gotProjectID, gotID)
+	}
+}
+
+func TestDeleteExtensionTreatsCodedNotFoundAsSuccess(t *testing.T) {
+	t.Parallel()
+
+	diags := deleteExtension(context.Background(), fakeExtensionDeleter{
+		delete: func(ctx context.Context, projectID, id string) error {
+			return extensionAPIErrorForTest(t, http.StatusNotFound, `{"code":"not_found"}`)
+		},
+	}, extensionModel{ID: types.StringValue("extension_123"), ProjectID: types.StringNull()})
+	if diags.HasError() {
+		t.Fatalf("unexpected diagnostics: %v", diags)
+	}
+}
+
+func TestDeleteExtensionExplainsDurablePoolDependency(t *testing.T) {
+	t.Parallel()
+
+	diags := deleteExtension(context.Background(), fakeExtensionDeleter{
+		delete: func(ctx context.Context, projectID, id string) error {
+			return extensionAPIErrorForTest(t, http.StatusBadRequest, `{"code":"resource_in_use"}`)
+		},
+	}, extensionModel{ID: types.StringValue("extension_123"), ProjectID: types.StringNull()})
+	if !extensionDiagnosticContains(diags, "Delete Kernel Extension", "Remove the extension from those durable browser pool configurations") {
+		t.Fatalf("diagnostics = %v, want browser pool dependency guidance", diags)
+	}
+}
+
+func TestDeleteExtensionDoesNotMisclassifyGenericErrors(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]error{
+		"generic bad request": extensionAPIErrorForTest(t, http.StatusBadRequest, `{}`),
+		"generic not found":   extensionAPIErrorForTest(t, http.StatusNotFound, `{}`),
+		"transport failure":   errors.New("connection reset"),
+	}
+	for name, err := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			diags := deleteExtension(context.Background(), fakeExtensionDeleter{
+				delete: func(ctx context.Context, projectID, id string) error { return err },
+			}, extensionModel{ID: types.StringValue("extension_123"), ProjectID: types.StringNull()})
+			if !extensionDiagnosticContains(diags, "Delete Kernel Extension", "extension_123") {
+				t.Fatalf("diagnostics = %v, want generic delete error with ID", diags)
+			}
+		})
+	}
+}
+
+func TestDeleteExtensionRejectsInvalidStateBeforeCall(t *testing.T) {
+	t.Parallel()
+
+	for name, state := range map[string]extensionModel{
+		"missing id":      {ID: types.StringNull(), ProjectID: types.StringNull()},
+		"unknown project": {ID: types.StringValue("extension_123"), ProjectID: types.StringUnknown()},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			called := false
+			diags := deleteExtension(context.Background(), fakeExtensionDeleter{
+				delete: func(ctx context.Context, projectID, id string) error { called = true; return nil },
+			}, state)
+			if !diags.HasError() {
+				t.Fatal("expected invalid state diagnostic")
+			}
+			if called {
+				t.Fatal("DeleteExtension called for invalid state")
+			}
+		})
+	}
+}