diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java b/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java
new file mode 100644
index 0000000..afbf0d5
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java
@@ -0,0 +1,29 @@
+package org.onlab.onos.cluster;
+
+import java.util.Set;
+
+/**
+ * Service for obtaining information about the individual instances within
+ * the controller cluster.
+ */
+public interface ClusterService {
+
+    /**
+     * Returns the set of current cluster members.
+     *
+     * @return set of cluster members
+     */
+    Set<ControllerInstance> getInstances();
+
+    /**
+     * Returns the availability state of the specified controller instance.
+     *
+     * @return availability state
+     */
+    ControllerInstance.State getState(ControllerInstance instance);
+    // TODO: determine if this would be better attached to ControllerInstance directly
+
+
+    // addListener, removeListener
+
+}