diff --git a/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php b/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
index ef79967..3effe65 100644
--- a/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
+++ b/core/lib/Drupal/Core/Entity/Field/FieldDefinition.php
@@ -188,6 +188,14 @@ public function isFieldRequired() {
   }
 
   /**
+   * {@inheritdoc}
+   */
+  public function isFieldMultiple() {
+    $cardinality = $this->getFieldCardinality();
+    return ($cardinality == static::CARDINALITY_UNLIMITED) || ($cardinality > 1);
+  }
+
+  /**
    * Sets whether the field is required.
    *
    * @param bool $required
diff --git a/core/lib/Drupal/Core/Entity/Field/FieldDefinitionInterface.php b/core/lib/Drupal/Core/Entity/Field/FieldDefinitionInterface.php
index b8dc354..26a9c2c 100644
--- a/core/lib/Drupal/Core/Entity/Field/FieldDefinitionInterface.php
+++ b/core/lib/Drupal/Core/Entity/Field/FieldDefinitionInterface.php
@@ -54,6 +54,11 @@
 interface FieldDefinitionInterface {
 
   /**
+   * Value indicating a field accepts an unlimited number of values.
+   */
+  const CARDINALITY_UNLIMITED = -1;
+
+  /**
    * Returns the machine name of the field.
    *
    * This defines how the field data is accessed from the entity. For example,
@@ -151,7 +156,8 @@ public function getFieldDescription();
   /**
    * Returns the maximum number of items allowed for the field.
    *
-   * Possible values are positive integers or FIELD_CARDINALITY_UNLIMITED.
+   * Possible values are positive integers or
+   * FieldDefinitionInterface::CARDINALITY_UNLIMITED.
    *
    * @return integer
    *   The field cardinality.
@@ -170,6 +176,14 @@ public function getFieldCardinality();
   public function isFieldRequired();
 
   /**
+   * Returns whether the field can contain multiple items.
+   *
+   * @return bool
+   *   TRUE if the field can contain multiple items, FALSE otherwise.
+   */
+  public function isFieldMultiple();
+
+  /**
    * Returns the default value for the field in a newly created entity.
    *
    * @param \Drupal\Core\Entity\EntityInterface $entity
diff --git a/core/lib/Drupal/Core/Entity/FieldableDatabaseStorageController.php b/core/lib/Drupal/Core/Entity/FieldableDatabaseStorageController.php
index 07cf115..5497efb 100644
--- a/core/lib/Drupal/Core/Entity/FieldableDatabaseStorageController.php
+++ b/core/lib/Drupal/Core/Entity/FieldableDatabaseStorageController.php
@@ -871,7 +871,7 @@ protected function doLoadFieldItems($entities, $age) {
           $delta_count[$row->entity_id][$row->langcode] = 0;
         }
 
-        if ($field->getFieldCardinality() == FIELD_CARDINALITY_UNLIMITED || $delta_count[$row->entity_id][$row->langcode] < $field->getFieldCardinality()) {
+        if ($field->getFieldCardinality() == FieldInterface::CARDINALITY_UNLIMITED || $delta_count[$row->entity_id][$row->langcode] < $field->getFieldCardinality()) {
           $item = array();
           // For each column declared by the field, populate the item from the
           // prefixed database column.
@@ -953,7 +953,7 @@ protected function doSaveFieldItems(EntityInterface $entity, $update) {
           $query->values($record);
           $revision_query->values($record);
 
-          if ($field->getFieldCardinality() != FIELD_CARDINALITY_UNLIMITED && ++$delta_count == $field->getFieldCardinality()) {
+          if ($field->getFieldCardinality() != FieldInterface::CARDINALITY_UNLIMITED && ++$delta_count == $field->getFieldCardinality()) {
             break;
           }
         }
diff --git a/core/modules/edit/lib/Drupal/edit/Tests/EditAutocompleteTermTest.php b/core/modules/edit/lib/Drupal/edit/Tests/EditAutocompleteTermTest.php
index c89b346..7e63021 100644
--- a/core/modules/edit/lib/Drupal/edit/Tests/EditAutocompleteTermTest.php
+++ b/core/modules/edit/lib/Drupal/edit/Tests/EditAutocompleteTermTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\edit\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
@@ -83,7 +84,7 @@ function setUp() {
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
       // Set cardinality to unlimited for tagging.
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
index f07a6ee..a18e127 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\entity_reference\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
@@ -44,7 +45,7 @@ function setUp() {
         'target_type' => 'node',
       ),
       'type' => 'entity_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ))->save();
 
     entity_create('field_instance', array(
diff --git a/core/modules/field/field.form.inc b/core/modules/field/field.form.inc
index 6f99192..f7bcd6b 100644
--- a/core/modules/field/field.form.inc
+++ b/core/modules/field/field.form.inc
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 
 /**
  * Returns HTML for an individual form element.
@@ -24,7 +25,7 @@ function theme_field_multiple_value_form($variables) {
   $element = $variables['element'];
   $output = '';
 
-  if ($element['#cardinality'] > 1 || $element['#cardinality'] == FIELD_CARDINALITY_UNLIMITED) {
+  if ($element['#cardinality'] > 1 || $element['#cardinality'] == FieldDefinitionInterface::CARDINALITY_UNLIMITED) {
     $form_required_marker = array('#theme' => 'form_required_marker');
     $required = !empty($element['#required']) ? drupal_render($form_required_marker) : '';
     $table_id = drupal_html_id($element['#field_name'] . '_values');
@@ -173,7 +174,7 @@ function field_add_more_js($form, $form_state) {
   $element = NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -1));
 
   // Ensure the widget allows adding additional items.
-  if ($element['#cardinality'] != FIELD_CARDINALITY_UNLIMITED) {
+  if ($element['#cardinality'] != FieldDefinitionInterface::CARDINALITY_UNLIMITED) {
     return;
   }
 
diff --git a/core/modules/field/field.module b/core/modules/field/field.module
index 84fd041..0ec9d1d 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -76,11 +76,6 @@
  */
 
 /**
- * Value for field API indicating a field accepts an unlimited number of values.
- */
-const FIELD_CARDINALITY_UNLIMITED = -1;
-
-/**
  * Implements hook_help().
  */
 function field_help($path, $arg) {
diff --git a/core/modules/field/field.views.inc b/core/modules/field/field.views.inc
index aecc48c..d0889af 100644
--- a/core/modules/field/field.views.inc
+++ b/core/modules/field/field.views.inc
@@ -377,7 +377,7 @@ function field_views_field_default_views_data(FieldInterface $field) {
       }
 
       // Expose additional delta column for multiple value fields.
-      if ($field->getFieldCardinality() > 1 || $field->getFieldCardinality() == FIELD_CARDINALITY_UNLIMITED) {
+      if ($field->isFieldMultiple()) {
         $title_delta = t('@label (!name:delta)', array('@label' => $label, '!name' => $field_name));
         $title_short_delta = t('@label:delta', array('@label' => $label));
 
diff --git a/core/modules/field/lib/Drupal/field/Entity/Field.php b/core/modules/field/lib/Drupal/field/Entity/Field.php
index 4496e16..eca7a13 100644
--- a/core/modules/field/lib/Drupal/field/Entity/Field.php
+++ b/core/modules/field/lib/Drupal/field/Entity/Field.php
@@ -120,7 +120,8 @@ class Field extends ConfigEntityBase implements FieldInterface {
    * The field cardinality.
    *
    * The maximum number of values the field can hold. Possible values are
-   * positive integers or FIELD_CARDINALITY_UNLIMITED. Defaults to 1.
+   * positive integers or FieldDefinitionInterface::CARDINALITY_UNLIMITED.
+   * Defaults to 1.
    *
    * @var integer
    */
@@ -600,6 +601,14 @@ public function isFieldRequired() {
   /**
    * {@inheritdoc}
    */
+  public function isFieldMultiple() {
+    $cardinality = $this->getFieldCardinality();
+    return ($cardinality == static::CARDINALITY_UNLIMITED) || ($cardinality > 1);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getFieldDefaultValue(EntityInterface $entity) { }
 
   /**
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
index dea4c95..9dc1cba 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
@@ -587,6 +587,13 @@ public function isFieldRequired() {
   /**
    * {@inheritdoc}
    */
+  public function isFieldMultiple() {
+    return $this->field->isFieldMultiple();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getFieldDefaultValue(EntityInterface $entity) {
     if (!empty($this->default_value_function)) {
       $function = $this->default_value_function;
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
index 32bea80..f78dc56 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemList.php
@@ -7,8 +7,9 @@
 
 namespace Drupal\field\Plugin\Type\FieldType;
 
-use Drupal\Core\TypedData\TypedDataInterface;
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Entity\Field\FieldItemList;
+use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\field\Field as FieldAPI;
 
 /**
@@ -54,7 +55,7 @@ public function getConstraints() {
     // form submitted values, this can only happen with 'multiple value'
     // widgets.
     $cardinality = $this->getFieldDefinition()->getFieldCardinality();
-    if ($cardinality != FIELD_CARDINALITY_UNLIMITED) {
+    if ($cardinality != FieldDefinitionInterface::CARDINALITY_UNLIMITED) {
       $constraints[] = \Drupal::typedData()
         ->getValidationConstraintManager()
         ->create('Count', array(
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
index 564ec20..f04b439 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
@@ -150,7 +150,7 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
 
     // Determine the number of widgets to display.
     switch ($cardinality) {
-      case FIELD_CARDINALITY_UNLIMITED:
+      case FieldDefinitionInterface::CARDINALITY_UNLIMITED:
         $field_state = field_form_get_state($parents, $field_name, $form_state);
         $max = $field_state['items_count'];
         $is_multiple = TRUE;
@@ -213,7 +213,7 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
       );
 
       // Add 'add more' button, if not working with a programmed form.
-      if ($cardinality == FIELD_CARDINALITY_UNLIMITED && empty($form_state['programmed'])) {
+      if ($cardinality == FieldDefinitionInterface::CARDINALITY_UNLIMITED && empty($form_state['programmed'])) {
         $elements['add_more'] = array(
           '#type' => 'submit',
           '#name' => strtr($id_prefix, '-', '_') . '_add_more',
@@ -408,9 +408,7 @@ public function massageFormValues(array $values, array $form, array &$form_state
    *   The field values.
    */
   protected function sortItems(FieldItemListInterface $items) {
-    $cardinality = $this->fieldDefinition->getFieldCardinality();
-    $is_multiple = ($cardinality == FIELD_CARDINALITY_UNLIMITED) || ($cardinality > 1);
-    if ($is_multiple && isset($items[0]->_weight)) {
+    if ($this->fieldDefinition->isFieldMultiple() && isset($items[0]->_weight)) {
       $itemValues = $items->getValue(TRUE);
       usort($itemValues, function ($a, $b) {
         $a_weight = (is_array($a) ? $a['_weight'] : 0);
diff --git a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
index 9779733..b0ccc85 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\field\Plugin\views\field;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Entity\FieldableDatabaseStorageController;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
@@ -130,7 +131,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
     $this->limit_values = FALSE;
 
     $cardinality = $field->getFieldCardinality();
-    if ($cardinality > 1 || $cardinality == FIELD_CARDINALITY_UNLIMITED) {
+    if ($field->isFieldMultiple()) {
       $this->multiple = TRUE;
 
       // If "Display all values in the same row" is FALSE, then we always limit
@@ -487,7 +488,7 @@ function multiple_options_form(&$form, &$form_state) {
     // translating prefix and suffix separately.
     list($prefix, $suffix) = explode('@count', t('Display @count value(s)'));
 
-    if ($field->getFieldCardinality() == FIELD_CARDINALITY_UNLIMITED) {
+    if ($field->getFieldCardinality() == FieldDefinitionInterface::CARDINALITY_UNLIMITED) {
       $type = 'textfield';
       $options = NULL;
       $size = 5;
diff --git a/core/modules/field/lib/Drupal/field/Tests/FormTest.php b/core/modules/field/lib/Drupal/field/Tests/FormTest.php
index f9b37d5..73b1e59 100644
--- a/core/modules/field/lib/Drupal/field/Tests/FormTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FormTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\field\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 class FormTest extends FieldTestBase {
 
   /**
@@ -73,7 +75,7 @@ function setUp() {
       'name' => 'field_unlimited',
       'entity_type' => 'entity_test',
       'type' => 'test_field',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     );
 
     $this->instance = array(
diff --git a/core/modules/field/lib/Drupal/field/Tests/NestedFormTest.php b/core/modules/field/lib/Drupal/field/Tests/NestedFormTest.php
index ad2b958..dd8e164 100644
--- a/core/modules/field/lib/Drupal/field/Tests/NestedFormTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/NestedFormTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\field\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 class NestedFormTest extends FieldTestBase {
 
   /**
@@ -39,7 +41,7 @@ public function setUp() {
       'name' => 'field_unlimited',
       'entity_type' => 'entity_test',
       'type' => 'test_field',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     );
 
     $this->instance = array(
diff --git a/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php b/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
index 7f157e2..6cf7c88 100644
--- a/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\field\Tests\Views;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 use Drupal\views\ViewExecutable;
 
@@ -51,7 +52,7 @@ protected function setUp() {
       'name' => 'field_name_3',
       'entity_type' => 'node',
       'type' => 'text',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ));
     $field->save();
     // Setup a field that will have no value.
@@ -59,7 +60,7 @@ protected function setUp() {
       'name' => 'field_name_4',
       'entity_type' => 'node',
       'type' => 'text',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ));
     $field->save();
 
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
index ebbd84c..d01be78 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
@@ -123,13 +123,13 @@ public function buildForm(array $form, array &$form_state, FieldInstanceInterfac
       '#title_display' => 'invisible',
       '#options' => array(
         'number' => $this->t('Limited'),
-        FIELD_CARDINALITY_UNLIMITED => $this->t('Unlimited'),
+        FieldInstanceInterface::CARDINALITY_UNLIMITED => $this->t('Unlimited'),
       ),
-      '#default_value' => ($cardinality == FIELD_CARDINALITY_UNLIMITED) ? FIELD_CARDINALITY_UNLIMITED : 'number',
+      '#default_value' => ($cardinality == FieldInstanceInterface::CARDINALITY_UNLIMITED) ? FieldInstanceInterface::CARDINALITY_UNLIMITED : 'number',
     );
     $form['field']['cardinality_container']['cardinality_number'] = array(
       '#type' => 'number',
-      '#default_value' => $cardinality != FIELD_CARDINALITY_UNLIMITED ? $cardinality : 1,
+      '#default_value' => $cardinality != FieldInstanceInterface::CARDINALITY_UNLIMITED ? $cardinality : 1,
       '#min' => 1,
       '#title' => $this->t('Limit'),
       '#title_display' => 'invisible',
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
index 1a8f65e..6c5931b 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\field_ui\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 
 /**
@@ -199,12 +200,12 @@ function cardinalitySettings() {
 
     // Set to unlimited.
     $edit = array(
-      'field[cardinality]' => FIELD_CARDINALITY_UNLIMITED,
+      'field[cardinality]' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     );
     $this->drupalPostForm($field_edit_path, $edit, t('Save field settings'));
     $this->assertText('Updated field Body field settings.');
     $this->drupalGet($field_edit_path);
-    $this->assertFieldByXPath("//select[@name='field[cardinality]']", FIELD_CARDINALITY_UNLIMITED);
+    $this->assertFieldByXPath("//select[@name='field[cardinality]']", FieldDefinitionInterface::CARDINALITY_UNLIMITED);
     $this->assertFieldByXPath("//input[@name='field[cardinality_number]']", 1);
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
index b0ed274..486b71e 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\file\Plugin\field\widget;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 use Drupal\Core\Entity\Field\FieldItemListInterface;
 
@@ -74,7 +75,7 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
     // Determine the number of widgets to display.
     $cardinality = $this->fieldDefinition->getFieldCardinality();
     switch ($cardinality) {
-      case FIELD_CARDINALITY_UNLIMITED:
+      case FieldDefinitionInterface::CARDINALITY_UNLIMITED:
         $max = count($items);
         $is_multiple = TRUE;
         break;
@@ -121,7 +122,7 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
     }
 
     $empty_single_allowed = ($cardinality == 1 && $delta == 0);
-    $empty_multiple_allowed = ($cardinality == FIELD_CARDINALITY_UNLIMITED || $delta < $cardinality) && empty($form_state['programmed']);
+    $empty_multiple_allowed = ($cardinality == FieldDefinitionInterface::CARDINALITY_UNLIMITED || $delta < $cardinality) && empty($form_state['programmed']);
 
     // Add one more empty row for new uploads except when this is a programmed
     // multiple form as it is not necessary.
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldValidateTest.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldValidateTest.php
index 18bead4..24fa44b 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldValidateTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldValidateTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\file\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\field\Field;
 
 /**
@@ -52,7 +53,7 @@ function testRequired() {
 
     // Try again with a multiple value field.
     $field->delete();
-    $this->createFileField($field_name, 'node', $type_name, array('cardinality' => FIELD_CARDINALITY_UNLIMITED), array('required' => '1'));
+    $this->createFileField($field_name, 'node', $type_name, array('cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED), array('required' => '1'));
 
     // Try to post a new node without uploading a file in the multivalue field.
     $edit = array('title' => $this->randomName());
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileItemTest.php b/core/modules/file/lib/Drupal/file/Tests/FileItemTest.php
index 31396ca..764238b 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileItemTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileItemTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\file\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Entity\Field\FieldItemInterface;
 use Drupal\Core\Entity\Field\FieldItemListInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
@@ -48,7 +49,7 @@ public function setUp() {
       'name' => 'file_test',
       'entity_type' => 'entity_test',
       'type' => 'file',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ))->save();
     entity_create('field_instance', array(
       'entity_type' => 'entity_test',
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageItemTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageItemTest.php
index 4fd70f7..0a26e6a 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageItemTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageItemTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\image\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Entity\Field\FieldItemListInterface;
 use Drupal\Core\Entity\Field\FieldItemInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
@@ -52,7 +53,7 @@ public function setUp() {
       'name' => 'image_test',
       'entity_type' => 'entity_test',
       'type' => 'image',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ))->save();
     entity_create('field_instance', array(
       'entity_type' => 'entity_test',
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
index 2301789..e5279a3 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
@@ -58,8 +58,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     // Prepare some properties for the child methods to build the actual form
     // element.
     $this->required = $element['#required'];
-    $cardinality = $this->fieldDefinition->getFieldCardinality();
-    $this->multiple = ($cardinality == FIELD_CARDINALITY_UNLIMITED) || ($cardinality > 1);
+    $this->multiple = $this->fieldDefinition->isFieldMultiple();
     $this->has_value = isset($items[0]->{$this->column});
 
     // Add our custom validator.
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
index 38ee919..df377f2 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
@@ -7,6 +7,7 @@
 namespace Drupal\rdf\Tests\Field;
 
 use Drupal\rdf\Tests\Field\FieldRdfaTestBase;
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 
 /**
@@ -62,7 +63,7 @@ public function setUp() {
       'name' => $this->fieldName,
       'entity_type' => 'entity_test_render',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/TaxonomyTermFieldAttributesTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/TaxonomyTermFieldAttributesTest.php
index 9d62168..078681d 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/TaxonomyTermFieldAttributesTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/TaxonomyTermFieldAttributesTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\rdf\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\taxonomy\Tests\TaxonomyTestBase;
 
 /**
@@ -158,7 +159,7 @@ protected function createTaxonomyTermReferenceField($field_name, $vocabulary) {
       'name' => $field_name,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/system/lib/Drupal/system/Tests/Ajax/MultiFormTest.php b/core/modules/system/lib/Drupal/system/Tests/Ajax/MultiFormTest.php
index 7709d64..884a191 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Ajax/MultiFormTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Ajax/MultiFormTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\system\Tests\Ajax;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests Ajax-enabled forms functionality with multiple instances of the form.
  */
@@ -38,7 +40,7 @@ function setUp() {
       'name' => $field_name,
       'entity_type' => 'node',
       'type' => 'text',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     ))->save();
     entity_create('field_instance', array(
       'field_name' => $field_name,
diff --git a/core/modules/system/lib/Drupal/system/Tests/Form/RebuildTest.php b/core/modules/system/lib/Drupal/system/Tests/Form/RebuildTest.php
index 163e5df..9b1d860 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Form/RebuildTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Form/RebuildTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\Form;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -75,7 +76,7 @@ function testPreserveFormActionAfterAJAX() {
       'name' => $field_name,
       'entity_type' => 'node',
       'type' => 'text',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
     );
     entity_create('field_entity', $field)->save();
     $instance = array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/RssTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/RssTest.php
index 654ea15..5706120 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/RssTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/RssTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\taxonomy\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests the rendering of term reference fields in RSS feeds.
  */
@@ -39,7 +41,7 @@ function setUp() {
       'name' => $this->field_name,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
index 6c5f1ea..76d9eba 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\taxonomy\Tests;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Entity\Field\FieldItemListInterface;
 use Drupal\Core\Entity\Field\FieldItemInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
@@ -48,7 +49,7 @@ public function setUp() {
       'name' => 'field_test_taxonomy',
       'entity_type' => 'entity_test',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermFieldMultipleVocabularyTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermFieldMultipleVocabularyTest.php
index 9ddb3c4..7797d30 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermFieldMultipleVocabularyTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermFieldMultipleVocabularyTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\taxonomy\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests a taxonomy term reference field that allows multiple vocabularies.
  */
@@ -44,7 +46,7 @@ function setUp() {
       'name' => $this->field_name,
       'entity_type' => 'entity_test',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermIndexTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermIndexTest.php
index 686b4eb..785b922 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermIndexTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermIndexTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\taxonomy\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests the hook implementations that maintain the taxonomy index.
  */
@@ -35,7 +37,7 @@ function setUp() {
       'name' => $this->field_name_1,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
@@ -66,7 +68,7 @@ function setUp() {
       'name' => $this->field_name_2,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTest.php
index d11eefe..6acc860 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\taxonomy\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests for taxonomy term functions.
  */
@@ -31,7 +33,7 @@ function setUp() {
       'name' => $field_name,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
index fb501e5..ce0bf7c 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\taxonomy\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 
 /**
@@ -32,7 +33,7 @@ function setUp() {
       'name' => $this->field_name,
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
index 6e7d393..632f48c 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\taxonomy\Tests\Views;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 use Drupal\views\Tests\ViewTestBase;
 use Drupal\views\Tests\ViewTestData;
@@ -82,7 +83,7 @@ protected function mockStandardInstall() {
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
       // Set cardinality to unlimited for tagging.
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
index 34b348b..b483714 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\user\Tests;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
 use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
@@ -251,7 +252,7 @@ function testRegistrationWithUserFields() {
     $this->assertEqual($new_user->test_user_field->value, $value, 'The field value was correclty saved.');
 
     // Check that the 'add more' button works.
-    $field->cardinality = FIELD_CARDINALITY_UNLIMITED;
+    $field->cardinality = FieldDefinitionInterface::CARDINALITY_UNLIMITED;
     $field->save();
     foreach (array('js', 'nojs') as $js) {
       $this->drupalGet('user/register');
diff --git a/core/modules/views/lib/Drupal/views/Tests/Wizard/TaggedWithTest.php b/core/modules/views/lib/Drupal/views/Tests/Wizard/TaggedWithTest.php
index 497af62..96a4280 100644
--- a/core/modules/views/lib/Drupal/views/Tests/Wizard/TaggedWithTest.php
+++ b/core/modules/views/lib/Drupal/views/Tests/Wizard/TaggedWithTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\views\Tests\Wizard;
 
+use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+
 /**
  * Tests the ability of the views wizard to create views filtered by taxonomy.
  */
@@ -57,7 +59,7 @@ function setUp() {
       'name' => 'field_views_testing_tags',
       'entity_type' => 'node',
       'type' => 'taxonomy_term_reference',
-      'cardinality' => FIELD_CARDINALITY_UNLIMITED,
+      'cardinality' => FieldDefinitionInterface::CARDINALITY_UNLIMITED,
       'settings' => array(
         'allowed_values' => array(
           array(