diff --git a/core/lib/Drupal/Core/Annotation/ContextDefinition.php b/core/lib/Drupal/Core/Annotation/ContextDefinition.php
index 75fbc9b..18095b2 100644
--- a/core/lib/Drupal/Core/Annotation/ContextDefinition.php
+++ b/core/lib/Drupal/Core/Annotation/ContextDefinition.php
@@ -100,7 +100,7 @@ public function __construct(array $values) {
     // used in the classes they pass to.
     foreach (['label', 'description'] as $key) {
       // @todo Remove this workaround in https://www.drupal.org/node/2362727.
-      if (isset($values[$key]) && $values[$key]->get() instanceof TranslationWrapper) {
+      if (isset($values[$key]) && $values[$key] instanceof Translation && $values[$key]->get() instanceof TranslationWrapper) {
         $values[$key] = (string) $values[$key]->get();
       }
       else {
diff --git a/core/lib/Drupal/Core/Block/BlockBase.php b/core/lib/Drupal/Core/Block/BlockBase.php
index 5af5efa..b5f10da 100644
--- a/core/lib/Drupal/Core/Block/BlockBase.php
+++ b/core/lib/Drupal/Core/Block/BlockBase.php
@@ -10,6 +10,7 @@
 use Drupal\block\BlockInterface;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Cache\CacheableDependencyInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContextAwarePluginAssignmentTrait;
 use Drupal\Core\Plugin\ContextAwarePluginBase;
@@ -315,21 +316,39 @@ public function setTransliteration(TransliterationInterface $transliteration) {
    * {@inheritdoc}
    */
   public function getCacheContexts() {
-    return [];
+    $cache_contexts = [];
+    foreach ($this->getContextValues() as $key => $context) {
+      if ($context instanceof CacheableDependencyInterface) {
+        $cache_contexts = Cache::mergeContexts($cache_contexts, $context->getCacheContexts());
+      }
+    }
+    return $cache_contexts;
   }
 
   /**
    * {@inheritdoc}
    */
   public function getCacheTags() {
-    return [];
+    $cache_tags = [];
+    foreach ($this->getContextValues() as $key => $context) {
+      if ($context instanceof CacheableDependencyInterface) {
+        $cache_tags = Cache::mergeTags($cache_tags, $context->getCacheTags());
+      }
+    }
+    return $cache_tags;
   }
 
   /**
    * {@inheritdoc}
    */
   public function getCacheMaxAge() {
-    return (int)$this->configuration['cache']['max_age'];
+    $max_age = (int)$this->configuration['cache']['max_age'];
+    foreach ($this->getContextValues() as $key => $context) {
+      if ($context instanceof CacheableDependencyInterface) {
+        $max_age = Cache::mergeMaxAges($max_age, $context->getCacheMaxAge());
+      }
+    }
+    return $max_age;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Plugin/ContextAwarePluginAssignmentTrait.php b/core/lib/Drupal/Core/Plugin/ContextAwarePluginAssignmentTrait.php
index 88249f5..e3ae261 100644
--- a/core/lib/Drupal/Core/Plugin/ContextAwarePluginAssignmentTrait.php
+++ b/core/lib/Drupal/Core/Plugin/ContextAwarePluginAssignmentTrait.php
@@ -53,18 +53,19 @@ protected function addContextAssignmentElement(ContextAwarePluginInterface $plug
         ];
         $element['context_slot_title'] = [
           '#type' => 'item',
-          '#title' => $this->t('@context value:', ['@context' => ucfirst($context_slot)]),
+          '#title' => $definition->getLabel() ?: $context_slot,
           '#markup' => $options[$context_id],
         ];
       }
 
       if (count($options) > 1) {
-        // Remove the default value title because we have more than one value.
+        // The context display element is only useful when a single context is
+        // available, we have multiple and require user interaction.
         unset($element['context_slot_title']);
 
         $assignments = $plugin->getContextMapping();
         $element[$context_slot] = [
-          '#title' => $this->t('Select a @context value:', ['@context' => $context_slot]),
+          '#title' => $definition->getLabel() ?: $context_slot,
           '#type' => 'select',
           '#options' => $options,
           '#required' => $definition->isRequired(),
diff --git a/core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php b/core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php
index df86cf0..ec3046d 100644
--- a/core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php
+++ b/core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php
@@ -62,6 +62,10 @@ public function getContextMapping() {
    * {@inheritdoc}
    */
   public function setContextMapping(array $context_mapping) {
+    // The ContextAwarePluginAssignmentTrait adds a visual element to the
+    // context mapping when only one context is available. We should unset this
+    // before saving the context mapping.
+    unset($context_mapping['context_slot_title']);
     if ($this instanceof ConfigurablePluginInterface) {
       $configuration = $this->getConfiguration();
       $configuration['context_mapping'] = $context_mapping;
diff --git a/core/modules/aggregator/config/schema/aggregator.schema.yml b/core/modules/aggregator/config/schema/aggregator.schema.yml
index 80bcbb8..cb2837c 100644
--- a/core/modules/aggregator/config/schema/aggregator.schema.yml
+++ b/core/modules/aggregator/config/schema/aggregator.schema.yml
@@ -48,6 +48,7 @@ block.settings.aggregator_feed_block:
       type: mapping
       label: 'Context assignments'
       mapping:
+        # This will be stored in the format of 'aggregator.feed:$uuid'.
         feed:
           type: string
           label: 'Feed'
diff --git a/core/modules/aggregator/src/Entity/Feed.php b/core/modules/aggregator/src/Entity/Feed.php
index 6f4f3fc..5c74ed2 100644
--- a/core/modules/aggregator/src/Entity/Feed.php
+++ b/core/modules/aggregator/src/Entity/Feed.php
@@ -115,9 +115,9 @@ public static function postDelete(EntityStorageInterface $storage, array $entiti
     parent::postDelete($storage, $entities);
     if (\Drupal::moduleHandler()->moduleExists('block')) {
       // Make sure there are no active blocks for these feeds.
-      $context_ids = array_keys($entities);
-      foreach ($context_ids as $key => $value) {
-        $context_ids[$key] = 'aggregator.feed:' . $value;
+      $context_ids = [];
+      foreach ($entities as $key => $entity) {
+        $context_ids[$key] = 'aggregator.feed:' . $entity->uuid();
       }
       $ids = \Drupal::entityQuery('block')
         ->condition('plugin', 'aggregator_feed_block')
diff --git a/core/modules/aggregator/src/EventSubscriber/AggregatorFeedContext.php b/core/modules/aggregator/src/EventSubscriber/AggregatorFeedContext.php
index 09dd845..5a884e8 100644
--- a/core/modules/aggregator/src/EventSubscriber/AggregatorFeedContext.php
+++ b/core/modules/aggregator/src/EventSubscriber/AggregatorFeedContext.php
@@ -42,7 +42,7 @@ class AggregatorFeedContext extends BlockContextSubscriberBase {
   protected $themeManager;
 
   /**
-   * Constructs a new NodeRouteContext.
+   * Constructs a new AggregatorFeedContext.
    *
    * @param \Drupal\Core\Entity\EntityManagerInterface $entity_manager
    *   The entity manager.
@@ -64,11 +64,14 @@ public function onBlockActiveContext(BlockContextEvent $event) {
       $block_plugin = $block->getPlugin();
       if ($block_plugin instanceof ContextAwarePluginInterface) {
         $contexts = $block_plugin->getContextMapping();
-        list(, $fid) = explode(':', $contexts['feed'], 2);
-        $feed = $this->feedStorage->load($fid);
+        // The context mapping is stored as aggregator.feed:uuid, so we're just
+        // extracting the UUID so that we can load the specific feed object.
+        list(, $uuid) = explode(':', $contexts['feed'], 2);
+        $feeds = $this->feedStorage->loadByProperties(['uuid' => $uuid]);
+        $feed = reset($feeds);
         $context = new Context(new ContextDefinition('entity:aggregator_feed'));
         $context->setContextValue($feed);
-        $event->setContext('aggregator.feed:' . $feed->id(), $context);
+        $event->setContext('aggregator.feed:' . $feed->uuid(), $context);
       }
     }
   }
@@ -81,7 +84,7 @@ public function onBlockAdministrativeContext(BlockContextEvent $event) {
     foreach ($feeds as $feed) {
       $context = new Context(new ContextDefinition('entity:aggregator_feed', $feed->label()));
       $context->setContextValue($feed);
-      $event->setContext('aggregator.feed:' . $feed->id(), $context);
+      $event->setContext('aggregator.feed:' . $feed->uuid(), $context);
     }
   }
 
diff --git a/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php b/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php
index 7e178b4..58010a8 100644
--- a/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php
+++ b/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php
@@ -9,7 +9,6 @@
 
 use Drupal\aggregator\ItemStorageInterface;
 use Drupal\Core\Block\BlockBase;
-use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\Query\QueryInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
@@ -163,13 +162,4 @@ public function build() {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheTags() {
-    $cache_tags = parent::getCacheTags();
-    $feed = $this->getContextValue('feed');
-    return Cache::mergeTags($cache_tags, $feed->getCacheTags());
-  }
-
 }
diff --git a/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php b/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php
index e9f0fa3..ea8183d 100644
--- a/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php
+++ b/core/modules/aggregator/src/Tests/AggregatorRenderingTest.php
@@ -44,7 +44,7 @@ public function testBlockLinks() {
     $block = $this->drupalPlaceBlock("aggregator_feed_block", array('label' => 'feed-' . $feed->label()));
 
     // Configure the feed that should be displayed.
-    $block->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed->id()]);
+    $block->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed->uuid()]);
     $block->getPlugin()->setConfigurationValue('block_count', 2);
     $block->save();
 
diff --git a/core/modules/aggregator/src/Tests/DeleteFeedTest.php b/core/modules/aggregator/src/Tests/DeleteFeedTest.php
index 0dbf5e3..e91c08e 100644
--- a/core/modules/aggregator/src/Tests/DeleteFeedTest.php
+++ b/core/modules/aggregator/src/Tests/DeleteFeedTest.php
@@ -30,10 +30,10 @@ public function testDeleteFeed() {
 
     // Place a block for both feeds.
     $block = $this->drupalPlaceBlock('aggregator_feed_block');
-    $block->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed1->id()]);
+    $block->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed1->uuid()]);
     $block->save();
     $block2 = $this->drupalPlaceBlock('aggregator_feed_block');
-    $block2->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed2->id()]);
+    $block2->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed2->uuid()]);
     $block2->save();
 
     // Delete feed.
diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index 137d6e9..b3ae2f6 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -329,7 +329,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     // Call the plugin submit handler.
     $block = $entity->getPlugin();
     $block->submitConfigurationForm($form, $settings);
-    if ($block instanceof ContextAwarePluginInterface) {
+    if ($block instanceof ContextAwarePluginInterface && $block->getContextDefinitions()) {
       $context_mapping = $settings->getValue('context_mapping', []);
       $block->setContextMapping($context_mapping);
     }
@@ -343,7 +343,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       $condition_values = (new FormState())
         ->setValues($values);
       $condition->submitConfigurationForm($form, $condition_values);
-      if ($condition instanceof ContextAwarePluginInterface) {
+      if ($condition instanceof ContextAwarePluginInterface && $condition->getContextDefinitions()) {
         $context_mapping = isset($values['context_mapping']) ? $values['context_mapping'] : [];
         $condition->setContextMapping($context_mapping);
       }
diff --git a/core/modules/block/src/EventSubscriber/NodeRouteContext.php b/core/modules/block/src/EventSubscriber/NodeRouteContext.php
index 97cb0bb..ddbf846 100644
--- a/core/modules/block/src/EventSubscriber/NodeRouteContext.php
+++ b/core/modules/block/src/EventSubscriber/NodeRouteContext.php
@@ -61,7 +61,7 @@ public function onBlockActiveContext(BlockContextEvent $event) {
    * {@inheritdoc}
    */
   public function onBlockAdministrativeContext(BlockContextEvent $event) {
-    $context = new Context(new ContextDefinition('entity:node', $this->t('Node from route')));
+    $context = new Context(new ContextDefinition('entity:node', $this->t('Node from URL')));
     $event->setContext('node.node', $context);
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Annotation/ContextDefinitionTest.php b/core/tests/Drupal/Tests/Core/Annotation/ContextDefinitionTest.php
new file mode 100644
index 0000000..7f8382f
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Annotation/ContextDefinitionTest.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @file Contains \Drupal\Tests\Core\Annotation\ContextDefinitionTest.
+ */
+
+namespace Drupal\Tests\Core\Annotation;
+
+use Drupal\Core\Annotation\ContextDefinition;
+use Drupal\Core\Annotation\Translation;
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Annotation\ContextDefinition
+ * @group Annotation
+ */
+class ContextDefinitionTest extends UnitTestCase {
+
+  /**
+   * The translation manager used for testing.
+   *
+   * @var \Drupal\Core\StringTranslation\TranslationInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $translationManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    $this->translationManager = $this->getStringTranslationStub();
+  }
+
+  /**
+   * Test the ContextDefinition Annotation.
+   */
+  public function testContextDefinitionAnnotation() {
+    $container = new ContainerBuilder();
+    $container->set('string_translation', $this->translationManager);
+    \Drupal::setContainer($container);
+
+    $values = [
+      'value' => 'entity:node',
+      //'label' => new Translation(['value' => 'test']),
+      'label' => 'test',
+      'description' => 'test',
+    ];
+    $context_definition = new ContextDefinition($values);
+    $definition = $context_definition->get();
+    //throw new \Exception(print_r(, TRUE));
+    // If the label or description are not a Translation annotation instance,
+    // it should be replaced by NULL.
+    $this->assertNull($definition->getLabel());
+    $this->assertNull($definition->getDescription());
+
+    $values = [
+      'value' => 'entity:node',
+      'label' => new Translation(['value' => 'test']),
+      'description' => new Translation(['value' => 'test']),
+    ];
+    $context_definition = new ContextDefinition($values);
+    $definition = $context_definition->get();
+    //throw new \Exception(print_r(, TRUE));
+    // If the label or description are a Translation annotation instance, the
+    // translated string should be returned.
+    $this->assertEquals('test', $definition->getLabel());
+    $this->assertEquals('test', $definition->getDescription());
+  }
+
+}