diff --git a/core/src/main/java/io/grpc/internal/ServiceConfigState.java b/core/src/main/java/io/grpc/internal/ServiceConfigState.java
new file mode 100644
index 0000000000..da4c4ce101
--- /dev/null
+++ b/core/src/main/java/io/grpc/internal/ServiceConfigState.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright 2019 The gRPC 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 io.grpc.internal;
+
+import static com.google.common.base.Preconditions.checkState;
+
+import io.grpc.NameResolver.ConfigOrError;
+import javax.annotation.Nullable;
+
+/**
+ * {@link ServiceConfigState} holds the state of the current service config.  It must be mutated
+ * and read from {@link ManagedChannelImpl} constructor or the provided syncContext.
+ */
+final class ServiceConfigState {
+  @Nullable private final ConfigOrError defaultServiceConfig;
+  private final boolean lookUpServiceConfig;
+
+  // mutable state
+  @Nullable private ConfigOrError currentServiceConfigOrError;
+  // Has there been at least one update?
+  private boolean updated;
+
+  /**
+   * @param defaultServiceConfig The initial service config, or {@code null} if absent.
+   * @param lookUpServiceConfig {@code true} if service config updates might occur.
+   * @param syncCtx The synchronization context that this is accessed from.
+   */
+  ServiceConfigState(
+      @Nullable ManagedChannelServiceConfig defaultServiceConfig,
+      boolean lookUpServiceConfig) {
+    if (defaultServiceConfig == null) {
+      this.defaultServiceConfig = null;
+    } else {
+      this.defaultServiceConfig = ConfigOrError.fromConfig(defaultServiceConfig);
+    }
+    this.lookUpServiceConfig = lookUpServiceConfig;
+    if (!lookUpServiceConfig) {
+      this.currentServiceConfigOrError = this.defaultServiceConfig;
+    }
+  }
+
+  /**
+   * Returns {@code true} if it RPCs should wait on a service config resolution.  This can return
+   * {@code false} if:
+   *
+   * <ul>
+   *   <li>There is a valid service config from the name resolver
+   *   <li>There is a valid default service config and a service config error from the name
+   *       resolver
+   *   <li>No service config from the name resolver, and no intent to lookup a service config.
+   * </ul>
+   *
+   * <p>In the final case, the default service config may be present or absent, and will be the
+   * current service config.
+   */
+  boolean shouldWaitOnServiceConfig() {
+    return !(updated || !expectUpdates());
+  }
+
+  /**
+   * Gets the current service config or error.
+   *
+   * @throws IllegalStateException if the service config has not yet been updated.
+   */
+  @Nullable
+  ConfigOrError getCurrent() {
+    checkState(!shouldWaitOnServiceConfig(), "still waiting on service config");
+    return currentServiceConfigOrError;
+  }
+
+  void update(@Nullable ConfigOrError coe) {
+    checkState(expectUpdates(), "unexpected service config update");
+    boolean firstUpdate = !updated;
+    updated = true;
+    if (firstUpdate) {
+      if (coe == null) {
+        currentServiceConfigOrError = defaultServiceConfig;
+      } else if (coe.getError() != null) {
+        if (defaultServiceConfig != null) {
+          currentServiceConfigOrError = defaultServiceConfig;
+        } else {
+          currentServiceConfigOrError = coe;
+        }
+      } else {
+        assert coe.getConfig() != null;
+        currentServiceConfigOrError = coe;
+      }
+    } else {
+      if (coe == null) {
+        if (defaultServiceConfig != null) {
+          currentServiceConfigOrError = defaultServiceConfig;
+        } else {
+          currentServiceConfigOrError = null;
+        }
+      } else if (coe.getError() != null) {
+        if (currentServiceConfigOrError != null && currentServiceConfigOrError.getError() != null) {
+          currentServiceConfigOrError = coe;
+        } else {
+          // discard
+        }
+      } else {
+        assert coe.getConfig() != null;
+        currentServiceConfigOrError = coe;
+      }
+    }
+  }
+
+  boolean expectUpdates() {
+    return lookUpServiceConfig;
+  }
+}
diff --git a/core/src/test/java/io/grpc/internal/ServiceConfigStateTest.java b/core/src/test/java/io/grpc/internal/ServiceConfigStateTest.java
new file mode 100644
index 0000000000..996401218f
--- /dev/null
+++ b/core/src/test/java/io/grpc/internal/ServiceConfigStateTest.java
@@ -0,0 +1,450 @@
+/*
+ * Copyright 2019 The gRPC 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 io.grpc.internal;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.Truth.assertWithMessage;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import io.grpc.NameResolver.ConfigOrError;
+import io.grpc.Status;
+import io.grpc.internal.ManagedChannelServiceConfig.MethodInfo;
+import java.util.Collections;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Tests for {@link ServiceConfigState}.
+ */
+@RunWith(JUnit4.class)
+public class ServiceConfigStateTest {
+
+  private final ManagedChannelServiceConfig serviceConfig1 = new ManagedChannelServiceConfig(
+      Collections.<String, MethodInfo>emptyMap(),
+      Collections.<String, MethodInfo>emptyMap(),
+      null,
+      null);
+  private final ManagedChannelServiceConfig serviceConfig2 = new ManagedChannelServiceConfig(
+      Collections.<String, MethodInfo>emptyMap(),
+      Collections.<String, MethodInfo>emptyMap(),
+      null,
+      null);
+  private final ConfigOrError config1 = ConfigOrError.fromConfig(serviceConfig1);
+  private final ConfigOrError config2 = ConfigOrError.fromConfig(serviceConfig2);
+  private final Status serviceConfigError1 = Status.UNKNOWN.withDescription("bang");
+  private final Status serviceConfigError2 = Status.INTERNAL.withDescription("boom");
+  private final ConfigOrError error1 = ConfigOrError.fromError(serviceConfigError1);
+  private final ConfigOrError error2 = ConfigOrError.fromError(serviceConfigError2);
+  private final ManagedChannelServiceConfig noServiceConfig = null;
+  private final ConfigOrError noConfig = null;
+
+  @Test
+  public void noLookup_default() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, false);
+
+    assertFalse(scs.expectUpdates());
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void noLookup_default_allUpdatesFail() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, false);
+
+    try {
+      scs.update(error1);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    try {
+      scs.update(error1);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    try {
+      scs.update(noConfig);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void noLookup_noDefault() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, false);
+
+    assertFalse(scs.expectUpdates());
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void noLookup_noDefault_allUpdatesFail() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, false);
+
+    try {
+      scs.update(error1);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+
+    try {
+      scs.update(config2);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+
+    try {
+      scs.update(noConfig);
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("unexpected service config update");
+    }
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    assertTrue(scs.expectUpdates());
+    assertTrue(scs.shouldWaitOnServiceConfig());
+    try {
+      scs.getCurrent();
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("still waiting on service config");
+    }
+  }
+
+  @Test
+  public void lookup_noDefault_onError_onError() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(error1, scs.getCurrent());
+
+    scs.update(error2);
+    assertSame(error2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onError_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(error1, scs.getCurrent());
+
+    scs.update(noConfig);
+    assertNull(scs.getCurrent());
+
+    scs.update(error2);
+    assertNull(scs.getCurrent()); //ignores future errors
+  }
+
+  @Test
+  public void lookup_noDefault_onError_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(error1, scs.getCurrent());
+
+    scs.update(config1);
+    assertSame(config1, scs.getCurrent());
+
+    scs.update(error2);
+    assertSame(config1, scs.getCurrent()); //ignores future errors
+  }
+
+  @Test
+  public void lookup_noDefault_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onAbsent_onError() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+
+    scs.update(error1);
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onAbsent_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+
+    scs.update(noConfig);
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onAbsent_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertNull(scs.getCurrent());
+
+    scs.update(config1);
+    assertSame(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(config1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onPresent_onError() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(config1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config1, scs.getCurrent());
+
+    scs.update(error1);
+    assertSame(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onPresent_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(config1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config1, scs.getCurrent());
+
+    scs.update(noConfig);
+    assertNull(scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_noDefault_onPresent_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(noServiceConfig, true);
+
+    scs.update(config1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config1, scs.getCurrent());
+
+    scs.update(config2);
+    assertSame(config2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    assertTrue(scs.expectUpdates());
+    assertTrue(scs.shouldWaitOnServiceConfig());
+    try {
+      scs.getCurrent();
+      fail();
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("still waiting on service config");
+    }
+  }
+
+  @Test
+  public void lookup_default_onError() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onError_onError() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(error2);
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onError_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(noConfig);
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onError_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(error1);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(config2);
+    assertSame(config2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onAbsent_onError() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(error1);
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onAbsent_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(noConfig);
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onAbsent_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(noConfig);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSameConfig(config1, scs.getCurrent());
+
+    scs.update(config2);
+    assertSame(config2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(config2);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onPresent_onError() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(config2);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config2, scs.getCurrent());
+
+    scs.update(error1);
+    assertSame(config2, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onPresent_onAbsent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+
+    scs.update(config2);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config2, scs.getCurrent());
+
+    scs.update(noConfig);
+    assertSameConfig(config1, scs.getCurrent());
+  }
+
+  @Test
+  public void lookup_default_onPresent_onPresent() {
+    ServiceConfigState scs = new ServiceConfigState(serviceConfig1, true);
+    ManagedChannelServiceConfig serviceConfig3 = new ManagedChannelServiceConfig(
+        Collections.<String, MethodInfo>emptyMap(),
+        Collections.<String, MethodInfo>emptyMap(),
+        null,
+        null);
+    ConfigOrError config3 = ConfigOrError.fromConfig(serviceConfig3);
+
+    scs.update(config2);
+    assertFalse(scs.shouldWaitOnServiceConfig());
+    assertSame(config2, scs.getCurrent());
+
+    scs.update(config3);
+    assertSame(config3, scs.getCurrent());
+  }
+
+  private static void assertSameConfig(ConfigOrError expected, ConfigOrError actual) {
+    if (actual == null || expected == null) {
+      assertSame(expected, actual);
+    }
+    assertWithMessage(actual.toString()).that(actual.getConfig())
+        .isSameInstanceAs(expected.getConfig());
+  }
+}