diff --git a/README.txt b/README.txt
index 37ec0a3..9d9513c 100644
--- a/README.txt
+++ b/README.txt
@@ -288,6 +288,25 @@ includes/datasource_external.inc) which you can extend. For a minimal use case,
 you will then only have to define the available fields that can be retrieved by
 the server.
 
+- Data type
+  Hook: hook_search_api_data_type_info()
+
+You can specify new data types for indexing fields. These new types can then be
+selected on indexes' „Fields“ tabs. You just have to implement the hook,
+returning some information on your data type, and specify in your module's
+documentation the format of your data type and how it should be used.
+
+For a custom data type to have an effect, in most cases the server's service
+class has to support that data type. A service class can advertize its support
+of a data type by declaring support for the "search_api_data_type_TYPE" feature
+in its supportsFeature() method. If this support isn't declared, a fallback data
+type is automatically used instead of the custom one.
+
+If a field is indexed with a custom data type, its entry in the index's options
+array will have the selected type in "real_type", while "type" contains the
+fallback type (which is always one of the default data types, as returned by
+search_api_default_field_types().
+
 - Data-alter callbacks
   Interface: SearchApiAlterCallbackInterface
   Base class: SearchApiAbstractAlterCallback
diff --git a/includes/index_entity.inc b/includes/index_entity.inc
index 35f0769..7441e28 100644
--- a/includes/index_entity.inc
+++ b/includes/index_entity.inc
@@ -111,10 +111,13 @@ class SearchApiIndex extends Entity {
    *   - name: The human-readable name for the field.
    *   - indexed: Boolean indicating whether the field is indexed or not.
    *   - type: The type set for this field. One of the types returned by
-   *     search_api_field_types().
+   *     search_api_default_field_types().
+   *   - real_type: (optional) If a custom data type was selected for this
+   *     field, this type will be stored here, and "type" contain the fallback
+   *     default data type.
    *   - boost: A boost value for terms found in this field during searches.
    *     Usually only relevant for fulltext fields.
-   *   - entity_type (optional): If set, the type of this field is really an
+   *   - entity_type: (optional) If set, the type of this field is really an
    *     entity. The "type" key will then contain "integer", meaning that
    *     servers will ignore this and merely index the entity's ID. Components
    *     displaying this field, though, are advised to use the entity label
@@ -416,11 +419,21 @@ class SearchApiIndex extends Entity {
     }
 
     $fields = $this->options['fields'];
+    $custom_type_fields = array();
     foreach ($fields as $field => $info) {
       if (!$info['indexed']) {
         unset($fields[$field]);
       }
-      unset($fields[$field]['indexed']);
+      else {
+        if (isset($info['real_type'])) {
+          $custom_type = search_api_extract_inner_type($info['real_type']);
+          if ($this->server()->supportsFeature('search_api_data_type_' . $custom_type)) {
+            $fields[$field]['type'] = $info['real_type'];
+            $custom_type_fields[$custom_type][$field] = search_api_list_nesting_level($info['real_type']);
+          }
+        }
+        unset($fields[$field]['indexed']);
+      }
     }
     if (empty($fields)) {
       throw new SearchApiException(t("Couldn't index values on '!name' index (no fields selected)", array('!name' => $this->name)));
@@ -445,6 +458,19 @@ class SearchApiIndex extends Entity {
     $data = array();
     foreach ($items as $id => $item) {
       $data[$id] = search_api_extract_fields($this->entityWrapper($item), $fields);
+      foreach ($custom_type_fields as $type => $type_fields) {
+        $info = search_api_get_data_type_info($type);
+        if (isset($info['conversion callback']) && is_callable($info['conversion callback'])) {
+          $callback = $info['conversion callback'];
+          foreach ($type_fields as $field => $nesting_level) {
+            if (isset($data[$id][$field]['value'])) {
+              $value = $data[$id][$field]['value'];
+              $original_type = $data[$id][$field]['original_type'];
+              $data[$id][$field]['value'] = _search_api_convert_custom_type($callback, $value, $original_type, $type, $nesting_level);
+            }
+          }
+        }
+      }
     }
 
     $this->preprocessIndexItems($data);
diff --git a/search_api.admin.inc b/search_api.admin.inc
index 6854d83..4aba7a2 100644
--- a/search_api.admin.inc
+++ b/search_api.admin.inc
@@ -1459,6 +1459,7 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
   $types = array(0 => search_api_field_types());
   $fulltext_type = array(0 => 'text');
   $entity_types = entity_get_info();
+  $default_types = search_api_default_field_types();
   $boosts = drupal_map_assoc(array('0.1', '0.2', '0.3', '0.5', '0.8', '1.0', '2.0', '3.0', '5.0', '8.0', '13.0', '21.0'));
 
   $form_state['index'] = $index;
@@ -1493,7 +1494,7 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
       '#default_value' => $info['indexed'],
     );
     $inner_type = search_api_extract_inner_type($info['type']);
-    if (isset($types[0][$inner_type])) {
+    if (isset($default_types[$inner_type])) {
       // Determine the correct type options (i.e., with the correct nesting level).
       $level = search_api_list_nesting_level($info['type']);
       if (empty($types[$level])) {
@@ -1510,7 +1511,7 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
       $form['fields'][$key]['type'] = array(
         '#type' => 'select',
         '#options' => $types[$level],
-        '#default_value' => $info['type'],
+        '#default_value' => isset($info['real_type']) ? $info['real_type'] : $info['type'],
         '#states' => array(
           'visible' => array(
             $css_key . '-indexed' => array('checked' => TRUE),
@@ -1546,7 +1547,7 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
       );
       $form['fields'][$key]['entity_type'] = array(
         '#type' => 'value',
-        '#value' => search_api_extract_inner_type($info['type']),
+        '#value' => $inner_type,
       );
       $form['fields'][$key]['type_name'] = array(
         '#markup' => check_plain($entity_types[$inner_type]['label']),
@@ -1627,7 +1628,7 @@ function _search_api_admin_get_fields(SearchApiIndex $index, EntityMetadataWrapp
     // The list nesting level for entities with a certain prefix
   $nesting_levels = array('' => 0);
 
-  $types = search_api_field_types();
+  $types = search_api_default_field_types();
   $flat = array();
   while ($wrappers) {
     foreach ($wrappers as $prefix => $wrapper) {
@@ -1651,7 +1652,7 @@ function _search_api_admin_get_fields(SearchApiIndex $index, EntityMetadataWrapp
         $type = search_api_extract_inner_type($info['type']);
         // Treat Entity API type "token" as our "string" type.
         // Also let text fields with limited options be of type "string" by default.
-        if ($type == 'token' || ($type == 'text' && $value->optionsList('view'))) {
+        if ($type == 'token' || ($type == 'text' && !empty($info['options list']))) {
           // Inner type is changed to "string".
           $type = 'string';
           // Set the field type accordingly.
@@ -1672,7 +1673,9 @@ function _search_api_admin_get_fields(SearchApiIndex $index, EntityMetadataWrapp
             }
             else {
               // Else, only update the nesting level.
-              $flat[$key]['type'] = search_api_nest_type(search_api_extract_inner_type($flat[$key]['type']), $info['type']);
+              $set_type = search_api_extract_inner_type(isset($flat[$key]['real_type']) ? $flat[$key]['real_type'] : $flat[$key]['type']);
+              $flat[$key]['type'] = $info['type'];
+              $flat[$key]['real_type'] = search_api_nest_type($set_type, $info['type']);
             }
           }
           else {
@@ -1768,8 +1771,18 @@ function search_api_admin_index_fields_submit(array $form, array &$form_state) {
   $options = isset($index->options) ? $index->options : array();
   if ($form_state['values']['op'] == t('Save changes')) {
     $fields = $form_state['values']['fields'];
+    $default_types = search_api_default_field_types();
+    $custom_types = search_api_get_data_type_info();
     foreach ($fields as $name => &$field) {
+      // Don't store the description.
       unset($field['description']);
+      // For non-default types, set type to the fallback and only real_type to
+      // the custom type.
+      $inner_type = search_api_extract_inner_type($field['type']);
+      if (!isset($default_types[$inner_type])) {
+        $field['real_type'] = $field['type'];
+        $field['type'] = search_api_nest_type($custom_types[$inner_type]['fallback'], $field['type']);
+      }
     }
     $options['fields'] = $fields;
     $ret = $index->update(array('options' => $options));
diff --git a/search_api.api.php b/search_api.api.php
index e245a4d..f7506f3 100644
--- a/search_api.api.php
+++ b/search_api.api.php
@@ -129,7 +129,6 @@ function hook_search_api_item_type_info() {
  * @see hook_search_api_item_type_info()
  */
 function hook_search_api_item_type_info_alter(array &$infos) {
-  hook_entity_info_alter();
   // Adds a boolean value is_entity to all type options telling whether the item
   // type represents an entity type.
   foreach ($infos as $type => $info) {
@@ -138,6 +137,55 @@ function hook_search_api_item_type_info_alter(array &$infos) {
 }
 
 /**
+ * Define new data types for indexed properties.
+ *
+ * New data types will appear as new option for the „Type“ field on indexes'
+ * „Fields“ tabs. Whether choosing a custom data type will have any effect
+ * depends on the server on which the data is indexed.
+ *
+ * @return array
+ *   An array containing custom data type definitions, keyed by their type
+ *   identifier and containing the following keys:
+ *   - name: The human-readable name of the type.
+ *   - fallback: (optional) One of the default data types (the keys from
+ *     search_api_default_field_types()) which should be used as a fallback if
+ *     the server doesn't support this data type. Defaults to "string".
+ *   - conversion callback: (optional) If specified, a callback function for
+ *     converting raw values to the given type, if possible. For the contract
+ *     of such a callback, see example_data_type_conversion().
+ *
+ * @see hook_search_api_data_type_info_alter()
+ * @see search_api_get_data_type_info()
+ * @see example_data_type_conversion()
+ */
+function hook_search_api_data_type_info() {
+  return array(
+    'example_type' => array(
+      'name' => t('Example type'),
+      // Could be omitted, as "string" is the default.
+      'fallback' => 'string',
+      'conversion callback' => 'example_data_type_conversion',
+    ),
+  );
+}
+
+/**
+ * Alter the data type info.
+ *
+ * Modules may implement this hook to alter the information that defines a data
+ * type, or to add/remove some entirely. All properties that are available in
+ * hook_search_api_data_type_info() can be altered here.
+ *
+ * @param array $infos
+ *   The data type info array, keyed by type identifier.
+ *
+ * @see hook_search_api_data_type_info()
+ */
+function hook_search_api_data_type_info_alter(array &$infos) {
+  $infos['example_type']['name'] .= ' 2';
+}
+
+/**
  * Registers one or more callbacks that can be called at index time to add
  * additional data to the indexed items (e.g. comments or attachments to nodes),
  * alter the data in other forms or remove items from the array.
@@ -453,3 +501,35 @@ function hook_default_search_api_index_alter(array &$defaults) {
 /**
  * @} End of "addtogroup hooks".
  */
+
+/**
+ * Convert a raw value from an entity to a custom data type.
+ *
+ * This function will be called for fields of the specific data type to convert
+ * all individual values of the field to the correct format.
+ *
+ * @param $value
+ *   The raw, single value, as extracted from an entity wrapper.
+ * @param $original_type
+ *   The original Entity API type of the value.
+ * @param $type
+ *   The custom data type to which the value should be converted. Can be ignored
+ *   if the callback is only used for a single data type.
+ *
+ * @return
+ *   The converted value, if a conversion could be executed. NULL otherwise.
+ *
+ * @see hook_search_api_data_type_info()
+ */
+function example_data_type_conversion($value, $original_type, $type) {
+  if ($type === 'example_type') {
+    // The example_type type apparently requires a rather complex data format.
+    return array(
+      'value' => $value,
+      'original' => $original_type,
+    );
+  }
+  // Someone used this callback for another, unknown type. Return NULL.
+  // (Normally, you can just assume that the/a correct type is given.)
+  return NULL;
+}
diff --git a/search_api.module b/search_api.module
index 0d8d407..9f72778 100644
--- a/search_api.module
+++ b/search_api.module
@@ -1071,8 +1071,26 @@ function search_api_current_search($search_id = NULL, SearchApiQuery $query = NU
  * @return array
  *   An associative array with all recognized types as keys, mapped to their
  *   translated display names.
+ *
+ * @see search_api_default_field_types()
+ * @see search_api_get_data_type_info()
  */
 function search_api_field_types() {
+  $types = search_api_default_field_types();
+  foreach (search_api_get_data_type_info() as $id => $type) {
+    $types[$id] = $type['name'];
+  }
+  return $types;
+}
+
+/**
+ * Returns the default field types recognized by the Search API framework.
+ *
+ * @return array
+ *   An associative array with the default types as keys, mapped to their
+ *   translated display names.
+ */
+function search_api_default_field_types() {
   return array(
     'text' => t('Fulltext'),
     'string' => t('String'),
@@ -1086,6 +1104,38 @@ function search_api_field_types() {
 }
 
 /**
+ * Returns either all custom field type definitions, or a specific one.
+ *
+ * @param $type
+ *   If specified, the type whose definition should be returned.
+ *
+ * @return array
+ *   If $type was not given, an array containing all custom data types, in the
+ *   format specified by hook_search_api_data_type_info().
+ *   Otherwise, the definition for the given type, or NULL if it is unknown.
+ *
+ * @see hook_search_api_data_type_info()
+ */
+function search_api_get_data_type_info($type = NULL) {
+  $types = &drupal_static(__FUNCTION__);
+  if (!isset($types)) {
+    $default_types = search_api_default_field_types();
+    $types = module_invoke_all('search_api_data_type_info');
+    $types = $types ? $types : array();
+    foreach ($types as &$type_info) {
+      if (!isset($type_info['fallback']) || !isset($default_types[$type_info['fallback']])) {
+        $type_info['fallback'] = 'string';
+      }
+    }
+    drupal_alter('search_api_data_type_info', $types);
+  }
+  if (isset($type)) {
+    return isset($types[$type]) ? $types[$type] : NULL;
+  }
+  return $types;
+}
+
+/**
  * Returns either a list of all available service infos, or a specific one.
  *
  * @see hook_search_api_service_info()
@@ -1936,3 +1986,24 @@ function _search_api_wrapper_add_all_properties(EntityMetadataWrapper $wrapper,
   }
   return $property_info;
 }
+
+/**
+ * Helper function for converting data to a custom type.
+ */
+function _search_api_convert_custom_type($callback, $value, $original_type, $type, $nesting_level) {
+  if ($nesting_level == 0) {
+    return call_user_func($callback, $value, $original_type, $type);
+  }
+  if (!is_array($value)) {
+    return NULL;
+  }
+  --$nesting_level;
+  $values = array();
+  foreach ($value as $v) {
+    $v = _search_api_convert_custom_type($callback, $v, $original_type, $type, $nesting_level);
+    if (isset($v) && !(is_array($v) && !$v)) {
+      $values[] = $v;
+    }
+  }
+  return $values;
+}