diff --git a/core/src/main/kotlin/net/corda/core/node/services/IdentityService.kt b/core/src/main/kotlin/net/corda/core/node/services/IdentityService.kt
index f5b765fd8d..e3a17ba222 100644
--- a/core/src/main/kotlin/net/corda/core/node/services/IdentityService.kt
+++ b/core/src/main/kotlin/net/corda/core/node/services/IdentityService.kt
@@ -10,6 +10,11 @@ import net.corda.core.crypto.Party
  */
 interface IdentityService {
     fun registerIdentity(party: Party)
+    /**
+     * Get all identities known to the service. This is expensive, and [partyFromKey] or [partyFromName] should be
+     * used in preference where possible.
+     */
+    fun getAllIdentities(): Iterable<Party>
 
     // There is no method for removing identities, as once we are made aware of a Party we want to keep track of them
     // indefinitely. It may be that in the long term we need to drop or archive very old Party information for space,
diff --git a/node/src/main/kotlin/net/corda/node/services/identity/InMemoryIdentityService.kt b/node/src/main/kotlin/net/corda/node/services/identity/InMemoryIdentityService.kt
index fe247ace48..0c4ee18a6c 100644
--- a/node/src/main/kotlin/net/corda/node/services/identity/InMemoryIdentityService.kt
+++ b/node/src/main/kotlin/net/corda/node/services/identity/InMemoryIdentityService.kt
@@ -4,6 +4,7 @@ import net.corda.core.crypto.CompositeKey
 import net.corda.core.crypto.Party
 import net.corda.core.node.services.IdentityService
 import net.corda.core.serialization.SingletonSerializeAsToken
+import java.util.*
 import java.util.concurrent.ConcurrentHashMap
 import javax.annotation.concurrent.ThreadSafe
 
@@ -20,6 +21,9 @@ class InMemoryIdentityService() : SingletonSerializeAsToken(), IdentityService {
         nameToParties[party.name] = party
     }
 
+    // We give the caller a copy of the data set to avoid any locking problems
+    override fun getAllIdentities(): Iterable<Party> = ArrayList(keyToParties.values)
+
     override fun partyFromKey(key: CompositeKey): Party? = keyToParties[key]
     override fun partyFromName(name: String): Party? = nameToParties[name]
 }
diff --git a/node/src/test/kotlin/net/corda/node/services/InMemoryIdentityServiceTests.kt b/node/src/test/kotlin/net/corda/node/services/InMemoryIdentityServiceTests.kt
new file mode 100644
index 0000000000..f74e59cc33
--- /dev/null
+++ b/node/src/test/kotlin/net/corda/node/services/InMemoryIdentityServiceTests.kt
@@ -0,0 +1,50 @@
+package net.corda.node.services
+
+import net.corda.node.services.identity.InMemoryIdentityService
+import net.corda.testing.ALICE
+import net.corda.testing.ALICE_PUBKEY
+import net.corda.testing.BOB
+import net.corda.testing.BOB_PUBKEY
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+/**
+ * Tests for the in memory identity service.
+ */
+class InMemoryIdentityServiceTests {
+
+    @Test
+    fun `get all identities`() {
+        val service = InMemoryIdentityService()
+        assertNull(service.getAllIdentities().firstOrNull())
+        service.registerIdentity(ALICE)
+        var expected = setOf(ALICE)
+        var actual = service.getAllIdentities().toHashSet()
+        assertEquals(expected, actual)
+
+        // Add a second party and check we get both back
+        service.registerIdentity(BOB)
+        expected = setOf(ALICE, BOB)
+        actual = service.getAllIdentities().toHashSet()
+        assertEquals(expected, actual)
+    }
+
+    @Test
+    fun `get identity by key`() {
+        val service = InMemoryIdentityService()
+        assertNull(service.partyFromKey(ALICE_PUBKEY))
+        service.registerIdentity(ALICE)
+        assertEquals(ALICE, service.partyFromKey(ALICE_PUBKEY))
+        assertNull(service.partyFromKey(BOB_PUBKEY))
+    }
+
+    @Test
+    fun `get identity by name`() {
+        val service = InMemoryIdentityService()
+        assertNull(service.partyFromName(ALICE.name))
+        service.registerIdentity(ALICE)
+        assertEquals(ALICE, service.partyFromName(ALICE.name))
+        assertNull(service.partyFromName(BOB.name))
+    }
+}
\ No newline at end of file
diff --git a/test-utils/src/main/kotlin/net/corda/testing/node/MockServices.kt b/test-utils/src/main/kotlin/net/corda/testing/node/MockServices.kt
index 5633dd4dab..a99247b6ad 100644
--- a/test-utils/src/main/kotlin/net/corda/testing/node/MockServices.kt
+++ b/test-utils/src/main/kotlin/net/corda/testing/node/MockServices.kt
@@ -72,6 +72,7 @@ class MockIdentityService(val identities: List<Party>) : IdentityService, Single
         get() = synchronized(identities) { identities.associateBy { it.name } }
 
     override fun registerIdentity(party: Party) { throw UnsupportedOperationException() }
+    override fun getAllIdentities(): Iterable<Party> = ArrayList(keyToParties.values)
     override fun partyFromKey(key: CompositeKey): Party? = keyToParties[key]
     override fun partyFromName(name: String): Party? = nameToParties[name]
 }