diff --git a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
index 67cc15d..7df3ec1 100644
--- a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
+++ b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
@@ -146,16 +146,36 @@ public function getSettings() {
   }
 
   /**
-   * Sets field settings.
+   * {@inheritdoc}
    *
-   * @param array $settings
-   *   The value to set.
+   * Note that the method does not unset existing settings not specified in the
+   * incoming $settings array.
    *
-   * @return static
-   *   The object itself for chaining.
+   * For example:
+   * @code
+   *   // Given these are the default settings.
+   *   $field_definition->getSettings() === [
+   *     'fruit' => 'apple',
+   *     'season' => 'summer',
+   *   ];
+   *   // Change only the 'fruit' setting.
+   *   $field_definition->setSettings(['fruit' => 'banana']);
+   *   // The 'season' setting persists unchanged.
+   *   $field_definition->getSettings() === [
+   *     'fruit' => 'banana',
+   *     'season' => 'summer',
+   *   ];
+   * @endcode
+   *
+   * For clarity, it is preferred to use setSetting() if not all available
+   * settings are supplied.
    */
   public function setSettings(array $settings) {
-    $this->getItemDefinition()->setSettings($settings);
+    // Assign settings individiually, in order to keep the current values
+    // of settings not specified in $settings.
+    foreach ($settings as $setting_name => $setting) {
+      $this->getItemDefinition()->setSetting($setting_name, $setting);
+    }
     return $this;
   }
 
@@ -167,15 +187,7 @@ public function getSetting($setting_name) {
   }
 
   /**
-   * Sets a field setting.
-   *
-   * @param string $setting_name
-   *   The field setting to set.
-   * @param mixed $value
-   *   The value to set.
-   *
-   * @return static
-   *   The object itself for chaining.
+   * {@inheritdoc}
    */
   public function setSetting($setting_name, $value) {
     $this->getItemDefinition()->setSetting($setting_name, $value);
diff --git a/core/lib/Drupal/Core/Field/FieldConfigBase.php b/core/lib/Drupal/Core/Field/FieldConfigBase.php
index 3d6613e..da0bca8 100644
--- a/core/lib/Drupal/Core/Field/FieldConfigBase.php
+++ b/core/lib/Drupal/Core/Field/FieldConfigBase.php
@@ -350,7 +350,7 @@ public function getSettings() {
    * {@inheritdoc}
    */
   public function setSettings(array $settings) {
-    $this->settings = $settings;
+    $this->settings = $settings + $this->settings;
     return $this;
   }
 
diff --git a/core/lib/Drupal/Core/Field/FieldConfigInterface.php b/core/lib/Drupal/Core/Field/FieldConfigInterface.php
index 1357a1e..b802221 100644
--- a/core/lib/Drupal/Core/Field/FieldConfigInterface.php
+++ b/core/lib/Drupal/Core/Field/FieldConfigInterface.php
@@ -55,7 +55,29 @@ public function setDescription($description);
   public function setTranslatable($translatable);
 
   /**
-   * Sets field settings (overwrites existing settings).
+   * Sets field settings.
+   *
+   * Note that the method does not unset existing settings not specified in the
+   * incoming $settings array.
+   *
+   * For example:
+   * @code
+   *   // Given these are the default settings.
+   *   $field_definition->getSettings() === [
+   *     'fruit' => 'apple',
+   *     'season' => 'summer',
+   *   ];
+   *   // Change only the 'fruit' setting.
+   *   $field_definition->setSettings(['fruit' => 'banana']);
+   *   // The 'season' setting persists unchanged.
+   *   $field_definition->getSettings() === [
+   *     'fruit' => 'banana',
+   *     'season' => 'summer',
+   *   ];
+   * @endcode
+   *
+   * For clarity, it is preferred to use setSetting() if not all available
+   * settings are supplied.
    *
    * @param array $settings
    *   The array of field settings.
diff --git a/core/lib/Drupal/Core/Field/FieldStorageDefinitionInterface.php b/core/lib/Drupal/Core/Field/FieldStorageDefinitionInterface.php
index 3d15bca..8321f7d 100644
--- a/core/lib/Drupal/Core/Field/FieldStorageDefinitionInterface.php
+++ b/core/lib/Drupal/Core/Field/FieldStorageDefinitionInterface.php
@@ -57,19 +57,23 @@ public function getName();
   public function getType();
 
   /**
-   * Returns the field settings.
+   * Returns the storage settings.
    *
    * Each field type defines the settings that are meaningful for that type.
    * For example, a text field can define a 'max_length' setting, and an image
    * field can define a 'alt_field_required' setting.
    *
+   * The method always returns an array of all available settings for this field
+   * type, possibly with the default values merged in if values have not been
+   * provided for all available settings.
+   *
    * @return mixed[]
    *   An array of key/value pairs.
    */
   public function getSettings();
 
   /**
-   * Returns the value of a given field setting.
+   * Returns the value of a given storage setting.
    *
    * @param string $setting_name
    *   The setting name.
diff --git a/core/modules/field/src/Entity/FieldStorageConfig.php b/core/modules/field/src/Entity/FieldStorageConfig.php
index 5fff1aa..3da118a 100644
--- a/core/modules/field/src/Entity/FieldStorageConfig.php
+++ b/core/modules/field/src/Entity/FieldStorageConfig.php
@@ -565,7 +565,7 @@ public function setSetting($setting_name, $value) {
    * {@inheritdoc}
    */
   public function setSettings(array $settings) {
-    $this->settings = $settings;
+    $this->settings = $settings + $this->settings;
     return $this;
   }
 
diff --git a/core/modules/field/src/FieldStorageConfigInterface.php b/core/modules/field/src/FieldStorageConfigInterface.php
index 116517a..3f44818 100644
--- a/core/modules/field/src/FieldStorageConfigInterface.php
+++ b/core/modules/field/src/FieldStorageConfigInterface.php
@@ -96,10 +96,32 @@ public function setCardinality($cardinality);
   public function setSetting($setting_name, $value);
 
   /**
-   * Sets field settings (overwrites existing settings).
+   * Sets field storage settings.
+   *
+   * Note that the method does not unset existing settings not specified in the
+   * incoming $settings array.
+   *
+   * For example:
+   * @code
+   *   // Given these are the default settings.
+   *   $storage_definition->getSettings() === [
+   *     'fruit' => 'apple',
+   *     'season' => 'summer',
+   *   ];
+   *   // Change only the 'fruit' setting.
+   *   $storage_definition->setSettings(['fruit' => 'banana']);
+   *   // The 'season' setting persists unchanged.
+   *   $storage_definition->getSettings() === [
+   *     'fruit' => 'banana',
+   *     'season' => 'summer',
+   *   ];
+   * @endcode
+   *
+   * For clarity, it is preferred to use setSetting() if not all available
+   * settings are supplied.
    *
    * @param array $settings
-   *   The array of field settings.
+   *   The array of storage settings.
    *
    * @return $this
    */
diff --git a/core/modules/menu_link_content/src/Entity/MenuLinkContent.php b/core/modules/menu_link_content/src/Entity/MenuLinkContent.php
index abbc694..7d51ae2 100644
--- a/core/modules/menu_link_content/src/Entity/MenuLinkContent.php
+++ b/core/modules/menu_link_content/src/Entity/MenuLinkContent.php
@@ -261,9 +261,7 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setDescription(t('The text to be used for this link in the menu.'))
       ->setRequired(TRUE)
       ->setTranslatable(TRUE)
-      ->setSettings(array(
-        'max_length' => 255,
-      ))
+      ->setSetting('max_length', 255)
       ->setDisplayOptions('view', array(
         'label' => 'hidden',
         'type' => 'string',
@@ -279,9 +277,7 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setLabel(t('Description'))
       ->setDescription(t('Shown when hovering over the menu link.'))
       ->setTranslatable(TRUE)
-      ->setSettings(array(
-        'max_length' => 255,
-      ))
+      ->setSetting('max_length', 255)
       ->setDisplayOptions('view', array(
         'label' => 'hidden',
         'type' => 'string',
diff --git a/core/modules/system/src/Tests/Entity/EntityFieldTest.php b/core/modules/system/src/Tests/Entity/EntityFieldTest.php
index 5414730..5d93c78 100644
--- a/core/modules/system/src/Tests/Entity/EntityFieldTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityFieldTest.php
@@ -30,7 +30,7 @@ class EntityFieldTest extends EntityUnitTestBase  {
    *
    * @var array
    */
-  public static $modules = array('filter', 'text', 'node', 'user');
+  public static $modules = array('filter', 'text', 'node', 'user', 'field_test');
 
   /**
    * @var string
@@ -688,10 +688,8 @@ public function testEntityConstraintValidation() {
       ->save();
     $definition = BaseFieldDefinition::create('entity_reference')
       ->setLabel('Test entity')
-      ->setSettings(array(
-        'target_type' => 'node',
-        'target_bundle' => 'article',
-      ));
+      ->setSetting('target_type', 'node')
+      ->setSetting('target_bundle', 'article');
     $reference_field = \Drupal::TypedDataManager()->create($definition);
     $reference = $reference_field->appendItem(array('entity' => $node))->get('entity');
     $violations = $reference->validate();
diff --git a/core/modules/system/src/Tests/Field/FieldSettingsTest.php b/core/modules/system/src/Tests/Field/FieldSettingsTest.php
new file mode 100644
index 0000000..2c2a8e9
--- /dev/null
+++ b/core/modules/system/src/Tests/Field/FieldSettingsTest.php
@@ -0,0 +1,120 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\system\Tests\Field\FieldSettingsTest.
+ */
+
+namespace Drupal\system\Tests\Field;
+
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\system\Tests\Entity\EntityUnitTestBase;
+
+/**
+ * Tests field settings methods on field definition structures.
+ *
+ * @group Field
+ */
+class FieldSettingsTest extends EntityUnitTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('field', 'field_test');
+
+  /**
+   * @covers \Drupal\Core\Field\BaseFieldDefinition::getSettings()
+   * @covers \Drupal\Core\Field\BaseFieldDefinition::setSettings()
+   */
+  public function testBaseFieldSettings() {
+    $base_field = BaseFieldDefinition::create('test_field');
+
+    // Check that the default settings have been populated.
+    $expected_settings = [
+      'test_field_storage_setting' => 'dummy test string',
+      'changeable' => 'a changeable field storage setting',
+      'unchangeable' => 'an unchangeable field storage setting',
+      'translatable_storage_setting' => 'a translatable field storage setting',
+      'test_field_setting' => 'dummy test string',
+      'translatable_field_setting' => 'a translatable field setting',
+    ];
+    $this->assertEqual($base_field->getSettings(), $expected_settings);
+
+    // Change one single setting using setSettings(), and check that the other
+    // expected settings are still present.
+    $expected_settings['test_field_setting'] = 'another test string';
+    $base_field->setSettings(['test_field_setting' => $expected_settings['test_field_setting']]);
+    $this->assertEqual($base_field->getSettings(), $expected_settings);
+  }
+
+  /**
+   * @covers \Drupal\field\Entity\FieldStorageConfig::getSettings()
+   * @covers \Drupal\field\Entity\FieldStorageConfig::setSettings()
+   */
+  public function testConfigurableFieldStorageSettings() {
+    $field_storage = FieldStorageConfig::create([
+      'field_name' => 'test_field',
+      'entity_type' => 'entity_test',
+      'type' => 'test_field'
+    ]);
+
+    // Check that the default settings have been populated.
+    $expected_settings = [
+      'test_field_storage_setting' => 'dummy test string',
+      'changeable' => 'a changeable field storage setting',
+      'unchangeable' => 'an unchangeable field storage setting',
+      'translatable_storage_setting' => 'a translatable field storage setting',
+    ];
+    $this->assertEqual($field_storage->getSettings(), $expected_settings);
+
+    // Change one single setting using setSettings(), and check that the other
+    // expected settings are still present.
+    $expected_settings['test_field_storage_setting'] = 'another test string';
+    $field_storage->setSettings(['test_field_storage_setting' => $expected_settings['test_field_storage_setting']]);
+    $this->assertEqual($field_storage->getSettings(), $expected_settings);
+  }
+
+  /**
+   * @covers \Drupal\field\Entity\FieldStorageConfig::getSettings()
+   * @covers \Drupal\field\Entity\FieldStorageConfig::setSettings()
+   */
+  public function testConfigurableFieldSettings() {
+    $field_storage = FieldStorageConfig::create([
+      'field_name' => 'test_field',
+      'entity_type' => 'entity_test',
+      'type' => 'test_field'
+    ]);
+    $field = FieldConfig::create([
+      'field_storage' => $field_storage,
+      'bundle' => 'entity_test'
+    ]);
+    // Note: FieldConfig does not populate default settings until the config
+    // is saved.
+    // @todo Remove once https://www.drupal.org/node/2327883 is fixed.
+    $field->save();
+
+    // Check that the default settings have been populated. Note: getSettings()
+    // returns both storage and field settings.
+    $expected_settings = [
+      'test_field_storage_setting' => 'dummy test string',
+      'changeable' => 'a changeable field storage setting',
+      'unchangeable' => 'an unchangeable field storage setting',
+      'translatable_storage_setting' => 'a translatable field storage setting',
+      'test_field_setting' => 'dummy test string',
+      'translatable_field_setting' => 'a translatable field setting',
+      'field_setting_from_config_data' => TRUE,
+    ];
+    $this->assertEqual($field->getSettings(), $expected_settings);
+
+    // Change one single setting using setSettings(), and check that the other
+    // expected settings are still present.
+    $expected_settings['test_field_setting'] = 'another test string';
+    $field->setSettings(['test_field_setting' => $expected_settings['test_field_setting']]);
+    $this->assertEqual($field->getSettings(), $expected_settings);
+  }
+
+}
diff --git a/core/modules/views/tests/src/Unit/EntityViewsDataTest.php b/core/modules/views/tests/src/Unit/EntityViewsDataTest.php
index b8db4fe..9a65d6e 100644
--- a/core/modules/views/tests/src/Unit/EntityViewsDataTest.php
+++ b/core/modules/views/tests/src/Unit/EntityViewsDataTest.php
@@ -485,7 +485,7 @@ public function testDataTableFields() {
     $base_field_definitions = $this->setupBaseFields(EntityTestMul::baseFieldDefinitions($this->baseEntityType));
     $base_field_definitions['type'] = BaseFieldDefinition::create('entity_reference')
       ->setLabel('entity test type')
-      ->setSettings(array('target_type' => 'entity_test_bundle'))
+      ->setSetting('target_type', 'entity_test_bundle')
       ->setTranslatable(TRUE);
     $base_field_definitions = $this->setupBaseFields($base_field_definitions);
     $user_base_field_definitions = [