diff --git a/api/v1alpha4/index/cluster.go b/api/v1alpha4/index/cluster.go
new file mode 100644
index 000000000000..fcd895300bc2
--- /dev/null
+++ b/api/v1alpha4/index/cluster.go
@@ -0,0 +1,55 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+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
+
+    http://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 index
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/pkg/errors"
+	clusterv1 "sigs.k8s.io/cluster-api/api/v1alpha4"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+const (
+	// ClusterClassNameField is used by the Cluster controller to index Clusters by ClusterClass name.
+	ClusterClassNameField = "spec.topology.class"
+)
+
+// ByClusterClassName adds the cluster class name  index to the
+// managers cache.
+func ByClusterClassName(ctx context.Context, mgr ctrl.Manager) error {
+	if err := mgr.GetCache().IndexField(ctx, &clusterv1.Cluster{},
+		ClusterClassNameField,
+		clusterByClassName,
+	); err != nil {
+		return errors.Wrap(err, "error setting index field")
+	}
+	return nil
+}
+
+func clusterByClassName(o client.Object) []string {
+	cluster, ok := o.(*clusterv1.Cluster)
+	if !ok {
+		panic(fmt.Sprintf("Expected Cluster but got a %T", o))
+	}
+	if cluster.Spec.Topology != nil {
+		return []string{cluster.Spec.Topology.Class}
+	}
+	return nil
+}
diff --git a/api/v1alpha4/index/cluster_test.go b/api/v1alpha4/index/cluster_test.go
new file mode 100644
index 000000000000..6976e4b1f0ba
--- /dev/null
+++ b/api/v1alpha4/index/cluster_test.go
@@ -0,0 +1,58 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+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
+
+    http://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 index
+
+import (
+	"testing"
+
+	. "github.com/onsi/gomega"
+	clusterv1 "sigs.k8s.io/cluster-api/api/v1alpha4"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+func TestClusterByClassName(t *testing.T) {
+	testCases := []struct {
+		name     string
+		object   client.Object
+		expected []string
+	}{
+		{
+			name:     "when cluster has no Topology",
+			object:   &clusterv1.Cluster{},
+			expected: nil,
+		},
+		{
+			name: "when cluster has a valid Topology",
+			object: &clusterv1.Cluster{
+				Spec: clusterv1.ClusterSpec{
+					Topology: &clusterv1.Topology{
+						Class: "class1",
+					},
+				},
+			},
+			expected: []string{"class1"},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.name, func(t *testing.T) {
+			g := NewWithT(t)
+			got := clusterByClassName(test.object)
+			g.Expect(got).To(Equal(test.expected))
+		})
+	}
+}
diff --git a/api/v1alpha4/index/index.go b/api/v1alpha4/index/index.go
index 4a0df4375921..fdbed5663d27 100644
--- a/api/v1alpha4/index/index.go
+++ b/api/v1alpha4/index/index.go
@@ -20,6 +20,7 @@ package index
 import (
 	"context"
 
+	"sigs.k8s.io/cluster-api/feature"
 	ctrl "sigs.k8s.io/controller-runtime"
 )
 
@@ -29,10 +30,15 @@ func AddDefaultIndexes(ctx context.Context, mgr ctrl.Manager) error {
 		return err
 	}
 
-	//nolint:revive
 	if err := ByMachineProviderID(ctx, mgr); err != nil {
 		return err
 	}
 
+	if feature.Gates.Enabled(feature.ClusterTopology) {
+		if err := ByClusterClassName(ctx, mgr); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }