diff -u b/core/modules/field/field.crud.inc b/core/modules/field/field.crud.inc
--- b/core/modules/field/field.crud.inc
+++ b/core/modules/field/field.crud.inc
@@ -169,10 +169,13 @@
     // Conditions.
     foreach ($params as $key => $value) {
       if ($key == 'storage.active') {
-        $checked_value = $field['storage']['active'];
+        $checked_value = $field->storage['active'];
+      }
+      else if($key == 'field_name') {
+        $checked_value = $field->id;
       }
       else {
-        $checked_value = $field[$key];
+        $checked_value = $field->$key;
       }
       if ($checked_value != $value) {
         continue 2;
@@ -182,11 +185,8 @@
     // Invoke read field.
     module_invoke_all('field_read_field', $field);
 
-    $field_name = $field['field_name'];
-    if ($include_deleted) {
-      $field_name = $field['uuid'];
-    }
-    $fields[$field_name] = $field;
+    $key = $include_deleted ? $field->uuid : $field->id;
+    $fields[$key] = $field;
   }
   return $fields;
 }
diff -u b/core/modules/field/lib/Drupal/field/FieldInfo.php b/core/modules/field/lib/Drupal/field/FieldInfo.php
--- b/core/modules/field/lib/Drupal/field/FieldInfo.php
+++ b/core/modules/field/lib/Drupal/field/FieldInfo.php
@@ -146,7 +146,7 @@
     foreach (config_get_storage_names_with_prefix('field.field') as $config_id) {
       $field_config = config($config_id)->get();
       if ($field_config['active'] && $field_config['storage']['active']) {
-        $fields[$field_config['field_name']] = $field_config;
+        $fields[$field_config['id']] = $field_config;
       }
     }
     // Get field instances.
@@ -197,7 +197,7 @@
     // Fill the name/ID map.
     foreach ($this->fieldsById as $field) {
       if (!$field['deleted']) {
-        $this->fieldIdsByName[$field['field_name']] = $field['uuid'];
+        $this->fieldIdsByName[$field['id']] = $field['uuid'];
       }
     }
 
diff -u b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
--- b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Core/Entity/Field.php
@@ -48,13 +48,6 @@
   public $uuid;
 
   /**
-   * The field name.
-   *
-   * @var string
-   */
-  public $field_name;
-
-  /**
    * The field type.
    *
    * @var string
@@ -153,14 +146,18 @@
     if (empty($values['type'])) {
       throw new FieldException('Attempt to create a field with no type.');
     }
-    if (empty($values['field_name'])) {
+    if (empty($values['field_name']) && empty($values['id'])) {
       throw new FieldException('Attempt to create an unnamed field.');
     }
-    if (!preg_match('/^[_a-z]+[_a-z0-9]*$/', $values['field_name'])) {
+    // Temporary BC layer: accept both 'id' and 'field_name'.
+    if (empty($values['id'])) {
+      $values['id'] = $values['field_name'];
+      unset($values['field_name']);
+    }
+    if (!preg_match('/^[_a-z]+[_a-z0-9]*$/', $values['id'])) {
       throw new FieldException('Attempt to create a field with invalid characters. Only lowercase alphanumeric characters and underscores are allowed, and only lowercase letters and underscore are allowed as the first character');
     }
 
-    $this->id = $values['field_name'];
 
     // Provide defaults.
     $values += array(
@@ -185,7 +182,6 @@
       'uuid',
       'status',
       'langcode',
-      'field_name',
       'type',
       'settings',
       'module',
@@ -217,18 +213,18 @@
       // Field name cannot be longer than 32 characters. We use drupal_strlen()
       // because the DB layer assumes that column widths are given in characters,
       // not bytes.
-      if (drupal_strlen($this->field_name) > 32) {
-        throw new FieldException(t('Attempt to create a field with a name longer than 32 characters: %name',
-          array('%name' => $this->field_name)));
+      if (drupal_strlen($this->id) > 32) {
+        throw new FieldException(t('Attempt to create a field with an ID longer than 32 characters: %id',
+          array('%id' => $this->id)));
       }
 
       // Ensure the field name is unique over active and disabled fields.
       // We do not care about deleted fields.
-      $prior_field = field_read_field($this->field_name, array('include_inactive' => TRUE));
+      $prior_field = field_read_field($this->id, array('include_inactive' => TRUE));
       if (!empty($prior_field)) {
         $message = $prior_field->active ?
-          t('Attempt to create field name %name which already exists and is active.', array('%name' => $this->field_name)):
-          t('Attempt to create field name %name which already exists, although it is inactive.', array('%name' => $this->field_name));
+          t('Attempt to create field %id which already exists and is active.', array('%id' => $this->id)):
+          t('Attempt to create field %id which already exists, although it is inactive.', array('%id' => $this->id));
         throw new FieldException($message);
       }
 
@@ -236,8 +232,8 @@
       // collisions with existing entity properties, but some is better
       // than none.
       foreach (\Drupal::service('plugin.manager.entity')->getDefinitions() as $type => $info) {
-        if (in_array($this->field_name, $info['entity_keys'])) {
-          throw new FieldException(t('Attempt to create field name %name which is reserved by entity type %type.', array('%name' => $this->field_name, '%type' => $type)));
+        if (in_array($this->id, $info['entity_keys'])) {
+          throw new FieldException(t('Attempt to create field %id which is reserved by entity type %type.', array('%id' => $this->id, '%type' => $type)));
         }
       }
 
@@ -328,7 +324,7 @@
         foreach ($bundles as $bundle) {
           // We need to get inactive instances too (e.g. the entity type is not
           // known anymore - case of comment.module being uninstalled).
-          $instance = field_read_instance($entity_type, $this->field_name, $bundle, array('include_inactive' => TRUE));
+          $instance = field_read_instance($entity_type, $this->id, $bundle, array('include_inactive' => TRUE));
           field_delete_instance($instance, FALSE);
         }
       }
@@ -404,8 +400,8 @@
   public function getBundles() {
     if (empty($this->deleted)) {
       $map = field_info_field_map();
-      if (isset($map[$this->field_name]['bundles'])) {
-        return $map[$this->field_name]['bundles'];
+      if (isset($map[$this->id]['bundles'])) {
+        return $map[$this->id]['bundles'];
       }
     }
     return array();
@@ -423,6 +419,9 @@
    */
   public function &offsetGet($offset) {
     switch ($offset) {
+      case 'field_name':
+        return $this->id;
+
       case 'columns':
         $this->getSchema();
         return $this->schema['columns'];
diff -u b/core/modules/field/tests/modules/field_test_config/config/field.field.field_test_import.yml b/core/modules/field/tests/modules/field_test_config/config/field.field.field_test_import.yml
--- b/core/modules/field/tests/modules/field_test_config/config/field.field.field_test_import.yml
+++ b/core/modules/field/tests/modules/field_test_config/config/field.field.field_test_import.yml
@@ -1,7 +1,6 @@
 id: field_test_import
 uuid: fb38277f-1fd4-49d5-8d09-9d7037fdcce9
 langcode: und
-field_name: field_test_import
 type: text
 settings:
   max_length: '255'
diff -u b/core/modules/field/tests/modules/field_test_config/staging/field.field.field_test_import_staging.yml b/core/modules/field/tests/modules/field_test_config/staging/field.field.field_test_import_staging.yml
--- b/core/modules/field/tests/modules/field_test_config/staging/field.field.field_test_import_staging.yml
+++ b/core/modules/field/tests/modules/field_test_config/staging/field.field.field_test_import_staging.yml
@@ -1,7 +1,6 @@
 id: field_test_import_staging
 uuid: 0bf654cc-f14a-4881-b94c-76959e47466b
 langcode: und
-field_name: field_test_import_staging
 type: text
 settings:
   max_length: '255'