diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index dbf888da4d..e0f0209ec5 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -917,6 +917,14 @@ phutil_register_library_map(array(
     'PhabricatorCrumbView' => 'view/layout/PhabricatorCrumbView.php',
     'PhabricatorCrumbsView' => 'view/layout/PhabricatorCrumbsView.php',
     'PhabricatorCursorPagedPolicyAwareQuery' => 'infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php',
+    'PhabricatorCustomField' => 'infrastructure/customfield/field/PhabricatorCustomField.php',
+    'PhabricatorCustomFieldDataNotAvailableException' => 'infrastructure/customfield/exception/PhabricatorCustomFieldDataNotAvailableException.php',
+    'PhabricatorCustomFieldImplementationIncompleteException' => 'infrastructure/customfield/exception/PhabricatorCustomFieldImplementationIncompleteException.php',
+    'PhabricatorCustomFieldIndexStorage' => 'infrastructure/customfield/storage/PhabricatorCustomFieldIndexStorage.php',
+    'PhabricatorCustomFieldNumericIndexStorage' => 'infrastructure/customfield/storage/PhabricatorCustomFieldNumericIndexStorage.php',
+    'PhabricatorCustomFieldStorage' => 'infrastructure/customfield/storage/PhabricatorCustomFieldStorage.php',
+    'PhabricatorCustomFieldStringIndexStorage' => 'infrastructure/customfield/storage/PhabricatorCustomFieldStringIndexStorage.php',
+    'PhabricatorCustomFieldValidationException' => 'infrastructure/customfield/exception/PhabricatorCustomFieldValidationException.php',
     'PhabricatorDaemon' => 'infrastructure/daemon/PhabricatorDaemon.php',
     'PhabricatorDaemonCombinedLogController' => 'applications/daemon/controller/PhabricatorDaemonCombinedLogController.php',
     'PhabricatorDaemonConsoleController' => 'applications/daemon/controller/PhabricatorDaemonConsoleController.php',
@@ -2753,6 +2761,13 @@ phutil_register_library_map(array(
     'PhabricatorCrumbView' => 'AphrontView',
     'PhabricatorCrumbsView' => 'AphrontView',
     'PhabricatorCursorPagedPolicyAwareQuery' => 'PhabricatorPolicyAwareQuery',
+    'PhabricatorCustomFieldDataNotAvailableException' => 'Exception',
+    'PhabricatorCustomFieldImplementationIncompleteException' => 'Exception',
+    'PhabricatorCustomFieldIndexStorage' => 'PhabricatorLiskDAO',
+    'PhabricatorCustomFieldNumericIndexStorage' => 'PhabricatorCustomFieldIndexStorage',
+    'PhabricatorCustomFieldStorage' => 'PhabricatorLiskDAO',
+    'PhabricatorCustomFieldStringIndexStorage' => 'PhabricatorCustomFieldIndexStorage',
+    'PhabricatorCustomFieldValidationException' => 'Exception',
     'PhabricatorDaemon' => 'PhutilDaemon',
     'PhabricatorDaemonCombinedLogController' => 'PhabricatorDaemonController',
     'PhabricatorDaemonConsoleController' => 'PhabricatorDaemonController',
diff --git a/src/infrastructure/customfield/exception/PhabricatorCustomFieldDataNotAvailableException.php b/src/infrastructure/customfield/exception/PhabricatorCustomFieldDataNotAvailableException.php
new file mode 100644
index 0000000000..26141dc506
--- /dev/null
+++ b/src/infrastructure/customfield/exception/PhabricatorCustomFieldDataNotAvailableException.php
@@ -0,0 +1,16 @@
+<?php
+
+final class PhabricatorCustomFieldDataNotAvailableException
+  extends Exception {
+
+  public function __construct(PhabricatorCustomField $field) {
+    $key = $field->getFieldKey();
+    $name = $field->getFieldName();
+    $class = get_class($field);
+
+    parent::__construct(
+      "Custom field '{$name}' (with key '{$key}', of class '{$class}') is ".
+      "attempting to access data which is not available in this context.");
+  }
+
+}
diff --git a/src/infrastructure/customfield/exception/PhabricatorCustomFieldImplementationIncompleteException.php b/src/infrastructure/customfield/exception/PhabricatorCustomFieldImplementationIncompleteException.php
new file mode 100644
index 0000000000..2d87c7e767
--- /dev/null
+++ b/src/infrastructure/customfield/exception/PhabricatorCustomFieldImplementationIncompleteException.php
@@ -0,0 +1,17 @@
+<?php
+
+final class PhabricatorCustomFieldImplementationIncompleteException
+  extends Exception {
+
+  public function __construct(PhabricatorCustomField $field) {
+    $key = $field->getFieldKey();
+    $name = $field->getFieldName();
+    $class = get_class($field);
+
+    parent::__construct(
+      "Custom field '{$name}' (with key '{$key}', of class '{$class}') is ".
+      "incompletely implemented: it claims to support a feature, but does not ".
+      "implement all of the required methods for that feature.");
+  }
+
+}
diff --git a/src/infrastructure/customfield/exception/PhabricatorCustomFieldValidationException.php b/src/infrastructure/customfield/exception/PhabricatorCustomFieldValidationException.php
new file mode 100644
index 0000000000..0cfc42251e
--- /dev/null
+++ b/src/infrastructure/customfield/exception/PhabricatorCustomFieldValidationException.php
@@ -0,0 +1,6 @@
+<?php
+
+final class PhabricatorCustomFieldValidationException
+  extends Exception {
+
+}
diff --git a/src/infrastructure/customfield/field/PhabricatorCustomField.php b/src/infrastructure/customfield/field/PhabricatorCustomField.php
new file mode 100644
index 0000000000..877f83ada2
--- /dev/null
+++ b/src/infrastructure/customfield/field/PhabricatorCustomField.php
@@ -0,0 +1,280 @@
+<?php
+
+/**
+ * @task context    Contextual Data
+ * @task storage    Field Storage
+ */
+abstract class PhabricatorCustomField {
+
+  private $viewer;
+
+  abstract public function getFieldKey();
+
+  public function getFieldIndex() {
+    return PhabricatorHash::digestForIndex($this->getFieldKey());
+  }
+
+  public function getFieldName() {
+    return $this->getFieldKey();
+  }
+
+  public function createFields() {
+    return array($this);
+  }
+
+  public function isFieldEnabled() {
+    return true;
+  }
+
+  public function canDisableField() {
+    return true;
+  }
+
+  public static function buildFieldList($base_class, array $spec) {
+    $this_class = __CLASS__;
+    if (!($base_class instanceof $this_class)) {
+      throw new Exception(
+        "Base class ('{$base_class}') must extend '{$this_class}'.");
+    }
+
+    $field_objects = id(new PhutilSymbolLoader())
+      ->setAncestorClass($base_class)
+      ->loadObjects();
+
+    $fields = array();
+    $from_map = array();
+    foreach ($field_objects as $field_object) {
+      $current_class = get_class($field_object);
+      foreach ($field_object->createFields() as $field) {
+        $key = $field->getFieldKey();
+        if (isset($fields[$key])) {
+          $original_class = $from_map[$key];
+          throw new Exception(
+            "Both '{$original_class}' and '{$current_class}' define a custom ".
+            "field with field key '{$key}'. Field keys must be unique.");
+        }
+        $from_map[$key] = $current_class;
+        $fields[$key] = $field;
+      }
+    }
+
+    foreach ($fields as $key => $field) {
+      if (!$field->isEnabled()) {
+        unset($fields[$key]);
+      }
+    }
+
+    $fields = array_select_keys($fields, array_keys($spec));
+
+    foreach ($spec as $key => $config) {
+      if (empty($fields[$key])) {
+        continue;
+      }
+      if (!empty($config['disabled'])) {
+        if ($fields[$key]->canDisableField()) {
+          unset($fields[$key]);
+        }
+      }
+    }
+
+    return $fields;
+  }
+
+
+/* -(  Contextual Data  )---------------------------------------------------- */
+
+
+  /**
+   * @task context
+   */
+  final public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+
+  /**
+   * @task context
+   */
+  final public function getViewer() {
+    return $this->viewer;
+  }
+
+
+  /**
+   * @task context
+   */
+  final protected function requireViewer() {
+    if (!$this->viewer) {
+      throw new PhabricatorCustomFieldDataNotAvailableException($this);
+    }
+    return $this->viewer;
+  }
+
+
+/* -(  Storage  )------------------------------------------------------------ */
+
+
+  /**
+   * Return a unique string used to key storage of this field's value, like
+   * "mycompany.fieldname" or similar. You can return null (the default) to
+   * indicate that this field does not use any storage.
+   *
+   * Fields which can be edited by the user will most commonly use storage,
+   * while some other types of fields (for instance, those which just display
+   * information in some stylized way) may not. Many builtin fields do not use
+   * storage because their data is available on the object itself.
+   *
+   * If you implement this, you must also implement @{method:getValueForStorage}
+   * and @{method:setValueFromStorage}.
+   *
+   * In most cases, a reasonable implementation is to simply reuse the field
+   * key:
+   *
+   *   return $this->getFieldKey();
+   *
+   * @return string|null  Unique key which identifies this field in auxiliary
+   *                      field storage. Alternatively, return null (default)
+   *                      to indicate that this field does not use storage.
+   * @task storage
+   */
+  public function getStorageKey() {
+    return null;
+  }
+
+
+  /**
+   * Return a serialized representation of the field value, appropriate for
+   * storing in auxiliary field storage. You must implement this method if
+   * you implement @{method:getStorageKey}.
+   *
+   * If the field value is a scalar, it can be returned unmodiifed. If not,
+   * it should be serialized (for example, using JSON).
+   *
+   * @return string Serialized field value.
+   * @task storage
+   */
+  public function getValueForStorage() {
+    throw new PhabricatorCustomFieldImplementationIncompleteException($this);
+  }
+
+
+  /**
+   * Set the field's value given a serialized storage value. This is called
+   * when the field is loaded; if no data is available, the value will be
+   * null. You must implement this method if you implement
+   * @{method:getStorageKey}.
+   *
+   * Usually, the value can be loaded directly. If it isn't a scalar, you'll
+   * need to undo whatever serialization you applied in
+   * @{method:getValueForStorage}.
+   *
+   * @param string|null Serialized field representation (from
+   *                    @{method:getValueForStorage}) or null if no value has
+   *                    ever been stored.
+   * @return this
+   * @task storage
+   */
+  public function setValueFromStorage($value) {
+    throw new PhabricatorCustomFieldImplementationIncompleteException($this);
+  }
+
+
+/* -(  ApplicationSearch  )-------------------------------------------------- */
+
+
+  /**
+   * Appearing in ApplicationSearch allows a field to be indexed and searched
+   * for.
+   *
+   * @return bool True to appear in ApplicationSearch.
+   * @task appsearch
+   */
+  public function shouldAppearInApplicationSearch() {
+    return false;
+  }
+
+
+  /**
+   * Return one or more indexes which this field can meaningfully query against
+   * to implement ApplicationSearch.
+   *
+   * Normally, you should build these using @{method:newStringIndex} and
+   * @{method:newNumericIndex}. For example, if a field holds a numeric value
+   * it might return a single numeric index:
+   *
+   *   return array($this->newNumericIndex($this->getValue()));
+   *
+   * If a field holds a more complex value (like a list of users), it might
+   * return several string indexes:
+   *
+   *   $indexes = array();
+   *   foreach ($this->getValue() as $phid) {
+   *     $indexes[] = $this->newStringIndex($phid);
+   *   }
+   *   return $indexes;
+   *
+   * @return list<PhabricatorCustomFieldIndexStorage> List of indexes.
+   * @task appsearch
+   */
+  public function buildFieldIndexes() {
+    return array();
+  }
+
+
+  /**
+   * Build a new empty storage object for storing string indexes. Normally,
+   * this should be a concrete subclass of
+   * @{class:PhabricatorCustomFieldStringIndexStorage}.
+   *
+   * @return PhabricatorCustomFieldStringIndexStorage Storage object.
+   * @task appsearch
+   */
+  protected function newStringIndexStorage() {
+    throw new PhabricatorCustomFieldImplementationIncompleteException($this);
+  }
+
+
+  /**
+   * Build a new empty storage object for storing string indexes. Normally,
+   * this should be a concrete subclass of
+   * @{class:PhabricatorCustomFieldStringIndexStorage}.
+   *
+   * @return PhabricatorCustomFieldStringIndexStorage Storage object.
+   * @task appsearch
+   */
+  protected function newNumericIndexStorage() {
+    throw new PhabricatorCustomFieldImplementationIncompleteException($this);
+  }
+
+
+  /**
+   * Build and populate storage for a string index.
+   *
+   * @param string String to index.
+   * @return PhabricatorCustomFieldStringIndexStorage Populated storage.
+   * @task appsearch
+   */
+  protected function newStringIndex($value) {
+    $key = $this->getFieldIndexKey();
+    return $this->newStringIndexStorage()
+      ->setIndexKey($key)
+      ->setIndexValue($value);
+  }
+
+
+  /**
+   * Build and populate storage for a numeric index.
+   *
+   * @param string Numeric value to index.
+   * @return PhabricatorCustomFieldNumericIndexStorage Populated storage.
+   * @task appsearch
+   */
+  protected function newNumericIndex($value) {
+    $key = $this->getFieldIndexKey();
+    return $this->newNumericIndexStorage()
+      ->setIndexKey($key)
+      ->setIndexValue($value);
+  }
+
+}
diff --git a/src/infrastructure/customfield/storage/PhabricatorCustomFieldIndexStorage.php b/src/infrastructure/customfield/storage/PhabricatorCustomFieldIndexStorage.php
new file mode 100644
index 0000000000..7a01fd4df7
--- /dev/null
+++ b/src/infrastructure/customfield/storage/PhabricatorCustomFieldIndexStorage.php
@@ -0,0 +1,18 @@
+<?php
+
+abstract class PhabricatorCustomFieldIndexStorage
+  extends PhabricatorLiskDAO {
+
+  protected $objectPHID;
+  protected $indexKey;
+  protected $indexValue;
+
+  public function getConfiguration() {
+    return array(
+      self::CONFIG_TIMESTAMPS => false,
+    ) + parent::getConfiguration();
+  }
+
+  abstract public function formatForInsert(AphrontDatabaseConnection $conn);
+
+}
diff --git a/src/infrastructure/customfield/storage/PhabricatorCustomFieldNumericIndexStorage.php b/src/infrastructure/customfield/storage/PhabricatorCustomFieldNumericIndexStorage.php
new file mode 100644
index 0000000000..f7d93456f8
--- /dev/null
+++ b/src/infrastructure/customfield/storage/PhabricatorCustomFieldNumericIndexStorage.php
@@ -0,0 +1,15 @@
+<?php
+
+abstract class PhabricatorCustomFieldNumericIndexStorage
+  extends PhabricatorCustomFieldIndexStorage {
+
+  public function formatForInsert(AphrontDatabaseConnection $conn) {
+    return qsprintf(
+      $conn,
+      '(%s, %s, %d)',
+      $this->getObjectPHID(),
+      $this->getIndexKey(),
+      $this->getIndexValue());
+  }
+
+}
diff --git a/src/infrastructure/customfield/storage/PhabricatorCustomFieldStorage.php b/src/infrastructure/customfield/storage/PhabricatorCustomFieldStorage.php
new file mode 100644
index 0000000000..31e3c25165
--- /dev/null
+++ b/src/infrastructure/customfield/storage/PhabricatorCustomFieldStorage.php
@@ -0,0 +1,16 @@
+<?php
+
+abstract class PhabricatorCustomFieldStorage
+  extends PhabricatorLiskDAO {
+
+  protected $objectPHID;
+  protected $fieldIndex;
+  protected $fieldValue;
+
+  public function getConfiguration() {
+    return array(
+      self::CONFIG_TIMESTAMPS => false,
+    ) + parent::getConfiguration();
+  }
+
+}
diff --git a/src/infrastructure/customfield/storage/PhabricatorCustomFieldStringIndexStorage.php b/src/infrastructure/customfield/storage/PhabricatorCustomFieldStringIndexStorage.php
new file mode 100644
index 0000000000..73ccc7597a
--- /dev/null
+++ b/src/infrastructure/customfield/storage/PhabricatorCustomFieldStringIndexStorage.php
@@ -0,0 +1,15 @@
+<?php
+
+abstract class PhabricatorCustomFieldStringIndexStorage
+  extends PhabricatorCustomFieldIndexStorage {
+
+  public function formatForInsert(AphrontDatabaseConnection $conn) {
+    return qsprintf(
+      $conn,
+      '(%s, %s, %s)',
+      $this->getObjectPHID(),
+      $this->getIndexKey(),
+      $this->getIndexValue());
+  }
+
+}