diff --git a/entity_translation.module b/entity_translation.module
index b34bafc..4c6fb4c 100644
--- a/entity_translation.module
+++ b/entity_translation.module
@@ -205,12 +205,44 @@ function entity_translation_menu_alter(&$items) {
     'module' => 'entity_translation',
   );
 
+  $items['admin/structure/types/manage/%/fields/%/translatable'] = array(
+    'title' => t('Confirm Change in translatability.'),
+    'description' => 'Confirm page for changing field translatability.',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('entity_translation_warning_form', 4, 6),
+    'access arguments' => array('administer entity translation'),
+  );
+
   // Node-specific menu alterations.
   entity_translation_node_menu_alter($items, $backup);
 
   return $items;
 }
 
+/*
+ * Confirm form for changing field translatability.
+ */
+function entity_translation_warning_form($form, &$form_state, $bundle, $field_name) {
+
+  $field = field_info_field($field_name);
+
+  $warning = t('By submitting this form you will trigger a batch operation.');
+  if ($field['translatable']) {
+    $warning .= "<br>" . t("<strong>All translations of this field will be deleted.</strong><br>Please backup your data before proceeding.");
+  }
+
+  $redirect = "admin/structure/types/manage/$bundle/fields/$field_name/field-settings";
+
+  $form = confirm_form($form, t('Warning.'), $redirect, $warning, t('Convert'), t('Cancel'));
+
+  $form['#submit'] = array('entity_translation_form_translatable_submit');
+
+  // We need to attach the field name for future processing.
+  $form['#etfield'] = $field;
+
+  return $form;
+}
+
 /**
  * Implements hook_admin_paths().
  */
@@ -481,16 +513,155 @@ function entity_translation_edit_form_submit($form, &$form_state) {
  * Enable a selector to choose whether a field is translatable.
  */
 function entity_translation_form_field_ui_field_settings_form_alter(&$form, $form_state) {
-  $instance = $form_state['build_info']['args'][0];
-  $field = field_info_field($instance['field_name']);
+  $field_name = $form_state['build_info']['args'][0]['field_name'];
+  $bundle = $form['#bundle'];
+
+  $path = "admin/structure/types/manage/$bundle/fields/$field_name/translatable";
   $form['field']['translatable'] = array(
-    '#type' => 'checkbox',
-    '#title' => t('Users may translate this field.'),
-    '#default_value' => $field['translatable'],
+    '#markup' => "<div>" . l(t('Change Translatability'), $path, array('query' => drupal_get_destination())) . "</div>",
   );
 }
 
 /**
+ * Submit handler for the field settings form.
+ *
+ * This submit handler maintains consistency between the translatability of an
+ * entity and the language under which the field data is stored. When a field is
+ * marked as translatable, all the data in $entity->{field_name}[LANGUAGE_NONE]
+ * is moved to $entity->{field_name}[$entity_language]. When a field is marked
+ * as untranslatable the opposite process occurs. Note that marking a field as
+ * untranslatable will cause all of its translations to be permanently removed,
+ * with the exception of the one corresponding to the entity language.
+ */
+function entity_translation_form_translatable_submit($form, $form_state) {
+  // This is the current state that we want to reverse.
+  $translatable = $form['#etfield']['translatable'];
+
+  $field_name = $form['#etfield']['field_name'];
+
+  // If a field is untranslatable, it can have no data except under LANGUAGE_NONE,
+  // Thus we need a field to be translatable before we convert data to the entity
+  // language. Conversely we need to convert data back to LANGUAGE_NONE before
+  // making a field untranslatable lest we lose information.
+  if ($translatable) {
+    $opts = array(
+      array('entity_translation_translatable_batch', array(!$translatable, $field_name)),
+      array('entity_translation_toggle_field_translatable', array($field_name)),
+    );
+  }
+  else {
+    $opts = array(
+      array('entity_translation_toggle_field_translatable', array($field_name)),
+      array('entity_translation_translatable_batch', array(!$translatable, $field_name)),
+    );
+  }
+
+  $batch = array(
+    'title' => t('Converting'),
+    'operations' => $opts,
+    'finished' => 'entity_translation_translatable_batch_done',
+  );
+
+  batch_set($batch);
+}
+
+/*
+ * Toggle translatability of given field.
+ *
+ * This is called from a batch operation, but should only run once per field.
+ */
+function entity_translation_toggle_field_translatable($field_name) {
+  $field = field_read_fields(array('field_name' => $field_name));
+
+  $field = $field[$field_name];
+  $field['translatable'] = !$field['translatable'];
+
+  field_update_field($field);
+}
+
+/**
+ * Batch operation. Convert field data to or from LANGUAGE_NONE.
+ */
+function entity_translation_translatable_batch($make_translatable, $field_name, &$context) {
+  if (empty($context['sandbox'])) {
+    $context['sandbox']['progress'] = 0;
+
+    // How many entities will need processing?
+    $query = new EntityFieldQuery();
+    $count = $query
+      ->fieldCondition($field_name)
+      ->count()
+      ->execute();
+
+    if (!$count) {
+      // Nothing to do.
+      $context['finished'] = 1;
+      return;
+    }
+
+    $context['sandbox']['max'] = $count;
+
+  }
+  // Number of entities to be processed for each step.
+  $limit = 10;
+
+  $query = new EntityFieldQuery();
+  $result = $query
+    ->fieldCondition($field_name)
+    ->range($context['sandbox']['progress'], $limit)
+    ->execute();
+
+  foreach ($result as $entity_type => $entities) {
+    foreach (entity_load($entity_type, array_keys($entities)) as $id => $entity) {
+      $context['sandbox']['progress']++;
+
+      $handler = entity_translation_get_handler($entity_type, $entity);
+      $langcode = $handler->getLanguage();
+
+      if ($make_translatable && isset($entity->{$field_name}[LANGUAGE_NONE])) {
+        // If the field is being switched to translatable and has data for
+        // LANGUAGE_NONE then we need to move the data to the right language.
+        $entity->{$field_name}[$langcode] = $entity->{$field_name}[LANGUAGE_NONE];
+        $entity->{$field_name}[LANGUAGE_NONE] = array();
+      }
+      elseif (!$make_translatable && isset($entity->{$field_name}[$langcode])) {
+        // The field has been marked untranslatable and has data in the entity
+        // language: we need to move it to LANGUAGE_NONE and drop the other
+        // translations.
+        $data = $entity->{$field_name}[$langcode];
+        foreach ($entity->{$field_name} as $lang => $items) {
+          // It's not enough to simply delete the field, we need to tell
+          // the translation handler to wipe it out.
+          $handler->removeTranslation($lang);
+        }
+        // Move the original field data to LANGUAGE_NONE
+        $entity->{$field_name}[LANGUAGE_NONE] = $data;
+      }
+      else {
+        // No need to save unchanged entities.
+        continue;
+      }
+      // Save field data.
+      field_attach_update($entity_type, $entity);
+    }
+  }
+  $context['finished'] = $context['sandbox']['progress']/$context['sandbox']['max'];
+}
+
+/**
+ * Check the exit status of the batch operation, and possibly resubmit the changed translatable status.
+ */
+function entity_translation_translatable_batch_done($success, $results, $operations) {
+  if ($success) {
+    drupal_set_message(t("Data successfully converted."));
+  }
+  else {
+    // TODO: Do something about this case.
+    drupal_set_message(t("Something went wrong when converting the data. Some nodes may appear to have lost fields."));
+  }
+}
+
+/**
  * Translation handler factory.
  *
  * @param $entity_type