diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -156,6 +156,7 @@
     'AphrontPageView' => 'view/page/AphrontPageView.php',
     'AphrontPlainTextResponse' => 'aphront/response/AphrontPlainTextResponse.php',
     'AphrontProgressBarView' => 'view/widget/bars/AphrontProgressBarView.php',
+    'AphrontProjectListHTTPParameterType' => 'aphront/httpparametertype/AphrontProjectListHTTPParameterType.php',
     'AphrontProxyResponse' => 'aphront/response/AphrontProxyResponse.php',
     'AphrontRedirectResponse' => 'aphront/response/AphrontRedirectResponse.php',
     'AphrontRedirectResponseTestCase' => 'aphront/response/__tests__/AphrontRedirectResponseTestCase.php',
@@ -179,6 +180,7 @@
     'AphrontTokenizerTemplateView' => 'view/control/AphrontTokenizerTemplateView.php',
     'AphrontTypeaheadTemplateView' => 'view/control/AphrontTypeaheadTemplateView.php',
     'AphrontUnhandledExceptionResponse' => 'aphront/response/AphrontUnhandledExceptionResponse.php',
+    'AphrontUserListHTTPParameterType' => 'aphront/httpparametertype/AphrontUserListHTTPParameterType.php',
     'AphrontView' => 'view/AphrontView.php',
     'AphrontWebpageResponse' => 'aphront/response/AphrontWebpageResponse.php',
     'ArcanistConduitAPIMethod' => 'applications/arcanist/conduit/ArcanistConduitAPIMethod.php',
@@ -2549,6 +2551,7 @@
     'PhabricatorPHID' => 'applications/phid/storage/PhabricatorPHID.php',
     'PhabricatorPHIDConstants' => 'applications/phid/PhabricatorPHIDConstants.php',
     'PhabricatorPHIDInterface' => 'applications/phid/interface/PhabricatorPHIDInterface.php',
+    'PhabricatorPHIDResolver' => 'applications/phid/resolver/PhabricatorPHIDResolver.php',
     'PhabricatorPHIDType' => 'applications/phid/type/PhabricatorPHIDType.php',
     'PhabricatorPHIDTypeTestCase' => 'applications/phid/type/__tests__/PhabricatorPHIDTypeTestCase.php',
     'PhabricatorPHPASTApplication' => 'applications/phpast/application/PhabricatorPHPASTApplication.php',
@@ -2738,6 +2741,7 @@
     'PhabricatorProjectObjectHasProjectEdgeType' => 'applications/project/edge/PhabricatorProjectObjectHasProjectEdgeType.php',
     'PhabricatorProjectOrUserDatasource' => 'applications/project/typeahead/PhabricatorProjectOrUserDatasource.php',
     'PhabricatorProjectOrUserFunctionDatasource' => 'applications/project/typeahead/PhabricatorProjectOrUserFunctionDatasource.php',
+    'PhabricatorProjectPHIDResolver' => 'applications/phid/resolver/PhabricatorProjectPHIDResolver.php',
     'PhabricatorProjectProfileController' => 'applications/project/controller/PhabricatorProjectProfileController.php',
     'PhabricatorProjectProjectHasMemberEdgeType' => 'applications/project/edge/PhabricatorProjectProjectHasMemberEdgeType.php',
     'PhabricatorProjectProjectHasObjectEdgeType' => 'applications/project/edge/PhabricatorProjectProjectHasObjectEdgeType.php',
@@ -2760,6 +2764,7 @@
     'PhabricatorProjectUserFunctionDatasource' => 'applications/project/typeahead/PhabricatorProjectUserFunctionDatasource.php',
     'PhabricatorProjectViewController' => 'applications/project/controller/PhabricatorProjectViewController.php',
     'PhabricatorProjectWatchController' => 'applications/project/controller/PhabricatorProjectWatchController.php',
+    'PhabricatorProjectsEditField' => 'applications/transactions/editfield/PhabricatorProjectsEditField.php',
     'PhabricatorProjectsPolicyRule' => 'applications/policy/rule/PhabricatorProjectsPolicyRule.php',
     'PhabricatorProtocolAdapter' => 'infrastructure/daemon/bot/adapter/PhabricatorProtocolAdapter.php',
     'PhabricatorPygmentSetupCheck' => 'applications/config/check/PhabricatorPygmentSetupCheck.php',
@@ -3040,6 +3045,7 @@
     'PhabricatorStreamingProtocolAdapter' => 'infrastructure/daemon/bot/adapter/PhabricatorStreamingProtocolAdapter.php',
     'PhabricatorSubscribableInterface' => 'applications/subscriptions/interface/PhabricatorSubscribableInterface.php',
     'PhabricatorSubscribedToObjectEdgeType' => 'applications/transactions/edges/PhabricatorSubscribedToObjectEdgeType.php',
+    'PhabricatorSubscribersEditField' => 'applications/transactions/editfield/PhabricatorSubscribersEditField.php',
     'PhabricatorSubscribersQuery' => 'applications/subscriptions/query/PhabricatorSubscribersQuery.php',
     'PhabricatorSubscriptionTriggerClock' => 'infrastructure/daemon/workers/clock/PhabricatorSubscriptionTriggerClock.php',
     'PhabricatorSubscriptionsAddSelfHeraldAction' => 'applications/subscriptions/herald/PhabricatorSubscriptionsAddSelfHeraldAction.php',
@@ -3154,6 +3160,7 @@
     'PhabricatorUserEmailTestCase' => 'applications/people/storage/__tests__/PhabricatorUserEmailTestCase.php',
     'PhabricatorUserLog' => 'applications/people/storage/PhabricatorUserLog.php',
     'PhabricatorUserLogView' => 'applications/people/view/PhabricatorUserLogView.php',
+    'PhabricatorUserPHIDResolver' => 'applications/phid/resolver/PhabricatorUserPHIDResolver.php',
     'PhabricatorUserPreferences' => 'applications/settings/storage/PhabricatorUserPreferences.php',
     'PhabricatorUserProfile' => 'applications/people/storage/PhabricatorUserProfile.php',
     'PhabricatorUserProfileEditor' => 'applications/people/editor/PhabricatorUserProfileEditor.php',
@@ -3166,6 +3173,7 @@
     'PhabricatorUserTestCase' => 'applications/people/storage/__tests__/PhabricatorUserTestCase.php',
     'PhabricatorUserTitleField' => 'applications/people/customfield/PhabricatorUserTitleField.php',
     'PhabricatorUserTransaction' => 'applications/people/storage/PhabricatorUserTransaction.php',
+    'PhabricatorUsersEditField' => 'applications/transactions/editfield/PhabricatorUsersEditField.php',
     'PhabricatorUsersPolicyRule' => 'applications/policy/rule/PhabricatorUsersPolicyRule.php',
     'PhabricatorUsersSearchField' => 'applications/people/searchfield/PhabricatorUsersSearchField.php',
     'PhabricatorVCSResponse' => 'applications/repository/response/PhabricatorVCSResponse.php',
@@ -3895,6 +3903,7 @@
     'AphrontPageView' => 'AphrontView',
     'AphrontPlainTextResponse' => 'AphrontResponse',
     'AphrontProgressBarView' => 'AphrontBarView',
+    'AphrontProjectListHTTPParameterType' => 'AphrontHTTPParameterType',
     'AphrontProxyResponse' => array(
       'AphrontResponse',
       'AphrontResponseProducerInterface',
@@ -3920,6 +3929,7 @@
     'AphrontTokenizerTemplateView' => 'AphrontView',
     'AphrontTypeaheadTemplateView' => 'AphrontView',
     'AphrontUnhandledExceptionResponse' => 'AphrontStandaloneHTMLResponse',
+    'AphrontUserListHTTPParameterType' => 'AphrontHTTPParameterType',
     'AphrontView' => array(
       'Phobject',
       'PhutilSafeHTMLProducerInterface',
@@ -6654,6 +6664,7 @@
     'PhabricatorPHDConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorPHID' => 'Phobject',
     'PhabricatorPHIDConstants' => 'Phobject',
+    'PhabricatorPHIDResolver' => 'Phobject',
     'PhabricatorPHIDType' => 'Phobject',
     'PhabricatorPHIDTypeTestCase' => 'PhutilTestCase',
     'PhabricatorPHPASTApplication' => 'PhabricatorApplication',
@@ -6891,6 +6902,7 @@
     'PhabricatorProjectObjectHasProjectEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorProjectOrUserDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'PhabricatorProjectOrUserFunctionDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
+    'PhabricatorProjectPHIDResolver' => 'PhabricatorPHIDResolver',
     'PhabricatorProjectProfileController' => 'PhabricatorProjectController',
     'PhabricatorProjectProjectHasMemberEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorProjectProjectHasObjectEdgeType' => 'PhabricatorEdgeType',
@@ -6916,6 +6928,7 @@
     'PhabricatorProjectUserFunctionDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'PhabricatorProjectViewController' => 'PhabricatorProjectController',
     'PhabricatorProjectWatchController' => 'PhabricatorProjectController',
+    'PhabricatorProjectsEditField' => 'PhabricatorTokenizerEditField',
     'PhabricatorProjectsPolicyRule' => 'PhabricatorPolicyRule',
     'PhabricatorProtocolAdapter' => 'Phobject',
     'PhabricatorPygmentSetupCheck' => 'PhabricatorSetupCheck',
@@ -7252,6 +7265,7 @@
     'PhabricatorStorageSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorStreamingProtocolAdapter' => 'PhabricatorProtocolAdapter',
     'PhabricatorSubscribedToObjectEdgeType' => 'PhabricatorEdgeType',
+    'PhabricatorSubscribersEditField' => 'PhabricatorTokenizerEditField',
     'PhabricatorSubscribersQuery' => 'PhabricatorQuery',
     'PhabricatorSubscriptionTriggerClock' => 'PhabricatorTriggerClock',
     'PhabricatorSubscriptionsAddSelfHeraldAction' => 'PhabricatorSubscriptionsHeraldAction',
@@ -7386,6 +7400,7 @@
       'PhabricatorPolicyInterface',
     ),
     'PhabricatorUserLogView' => 'AphrontView',
+    'PhabricatorUserPHIDResolver' => 'PhabricatorPHIDResolver',
     'PhabricatorUserPreferences' => 'PhabricatorUserDAO',
     'PhabricatorUserProfile' => 'PhabricatorUserDAO',
     'PhabricatorUserProfileEditor' => 'PhabricatorApplicationTransactionEditor',
@@ -7398,6 +7413,7 @@
     'PhabricatorUserTestCase' => 'PhabricatorTestCase',
     'PhabricatorUserTitleField' => 'PhabricatorUserCustomField',
     'PhabricatorUserTransaction' => 'PhabricatorApplicationTransaction',
+    'PhabricatorUsersEditField' => 'PhabricatorTokenizerEditField',
     'PhabricatorUsersPolicyRule' => 'PhabricatorPolicyRule',
     'PhabricatorUsersSearchField' => 'PhabricatorSearchTokenizerField',
     'PhabricatorVCSResponse' => 'AphrontResponse',
diff --git a/src/aphront/httpparametertype/AphrontProjectListHTTPParameterType.php b/src/aphront/httpparametertype/AphrontProjectListHTTPParameterType.php
new file mode 100644
--- /dev/null
+++ b/src/aphront/httpparametertype/AphrontProjectListHTTPParameterType.php
@@ -0,0 +1,42 @@
+<?php
+
+final class AphrontProjectListHTTPParameterType
+  extends AphrontHTTPParameterType {
+
+  protected function getParameterValue(AphrontRequest $request, $key) {
+    $type = new AphrontStringListHTTPParameterType();
+    $list = $this->getValueWithType($type, $request, $key);
+
+    return id(new PhabricatorProjectPHIDResolver())
+      ->setViewer($this->getViewer())
+      ->resolvePHIDs($list);
+  }
+
+  protected function getParameterTypeName() {
+    return 'list<project>';
+  }
+
+  protected function getParameterFormatDescriptions() {
+    return array(
+      pht('Comma-separated list of project PHIDs.'),
+      pht('List of project PHIDs, as array.'),
+      pht('Comma-separated list of project hashtags.'),
+      pht('List of project hashtags, as array.'),
+      pht('Mixture of hashtags and PHIDs.'),
+    );
+  }
+
+  protected function getParameterExamples() {
+    return array(
+      'v=PHID-PROJ-1111',
+      'v=PHID-PROJ-1111,PHID-PROJ-2222',
+      'v=hashtag',
+      'v=frontend,backend',
+      'v[]=PHID-PROJ-1111&v[]=PHID-PROJ-2222',
+      'v[]=frontend&v[]=backend',
+      'v=PHID-PROJ-1111,frontend',
+      'v[]=PHID-PROJ-1111&v[]=backend',
+    );
+  }
+
+}
diff --git a/src/aphront/httpparametertype/AphrontUserListHTTPParameterType.php b/src/aphront/httpparametertype/AphrontUserListHTTPParameterType.php
new file mode 100644
--- /dev/null
+++ b/src/aphront/httpparametertype/AphrontUserListHTTPParameterType.php
@@ -0,0 +1,42 @@
+<?php
+
+final class AphrontUserListHTTPParameterType
+  extends AphrontHTTPParameterType {
+
+  protected function getParameterValue(AphrontRequest $request, $key) {
+    $type = new AphrontStringListHTTPParameterType();
+    $list = $this->getValueWithType($type, $request, $key);
+
+    return id(new PhabricatorUserPHIDResolver())
+      ->setViewer($this->getViewer())
+      ->resolvePHIDs($list);
+  }
+
+  protected function getParameterTypeName() {
+    return 'list<user>';
+  }
+
+  protected function getParameterFormatDescriptions() {
+    return array(
+      pht('Comma-separated list of user PHIDs.'),
+      pht('List of user PHIDs, as array.'),
+      pht('Comma-separated list of usernames.'),
+      pht('List of usernames, as array.'),
+      pht('Mixture of usernames and PHIDs.'),
+    );
+  }
+
+  protected function getParameterExamples() {
+    return array(
+      'v=PHID-USER-1111',
+      'v=PHID-USER-1111,PHID-USER-2222',
+      'v=username',
+      'v=alincoln,htaft',
+      'v[]=PHID-USER-1111&v[]=PHID-USER-2222',
+      'v[]=htaft&v[]=alincoln',
+      'v=PHID-USER-1111,alincoln',
+      'v[]=PHID-USER-1111&v[]=htaft',
+    );
+  }
+
+}
diff --git a/src/applications/phid/resolver/PhabricatorPHIDResolver.php b/src/applications/phid/resolver/PhabricatorPHIDResolver.php
new file mode 100644
--- /dev/null
+++ b/src/applications/phid/resolver/PhabricatorPHIDResolver.php
@@ -0,0 +1,46 @@
+<?php
+
+/**
+ * Resolve a list of identifiers into PHIDs.
+ *
+ * This class simplifies the process of convering a list of mixed token types
+ * (like some PHIDs and some usernames) into a list of just PHIDs.
+ */
+abstract class PhabricatorPHIDResolver extends Phobject {
+
+  private $viewer;
+
+  final public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  final public function getViewer() {
+    return $this->viewer;
+  }
+
+  final public function resolvePHIDs(array $phids) {
+    $type_unknown = PhabricatorPHIDConstants::PHID_TYPE_UNKNOWN;
+
+    $names = array();
+    foreach ($phids as $key => $phid) {
+      if (phid_get_type($phid) == $type_unknown) {
+        $names[$key] = $phid;
+      }
+    }
+
+    if ($names) {
+      $map = $this->getResolutionMap($names);
+      foreach ($names as $key => $name) {
+        if (isset($map[$name])) {
+          $phids[$key] = $map[$name];
+        }
+      }
+    }
+
+    return $phids;
+  }
+
+  abstract protected function getResolutionMap(array $names);
+
+}
diff --git a/src/applications/phid/resolver/PhabricatorProjectPHIDResolver.php b/src/applications/phid/resolver/PhabricatorProjectPHIDResolver.php
new file mode 100644
--- /dev/null
+++ b/src/applications/phid/resolver/PhabricatorProjectPHIDResolver.php
@@ -0,0 +1,28 @@
+<?php
+
+final class PhabricatorProjectPHIDResolver
+  extends PhabricatorPHIDResolver {
+
+  protected function getResolutionMap(array $names) {
+    // This is a little awkward but we want to pick up the normalization
+    // rules from the PHIDType. This flow could perhaps be made cleaner.
+
+    foreach ($names as $key => $name) {
+      $names[$key] = '#'.$name;
+    }
+
+    $query = id(new PhabricatorObjectQuery())
+      ->setViewer($this->getViewer());
+
+    $projects = id(new PhabricatorProjectProjectPHIDType())
+      ->loadNamedObjects($query, $names);
+
+    $results = array();
+    foreach ($projects as $hashtag => $project) {
+      $results[substr($hashtag, 1)] = $project->getPHID();
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/phid/resolver/PhabricatorUserPHIDResolver.php b/src/applications/phid/resolver/PhabricatorUserPHIDResolver.php
new file mode 100644
--- /dev/null
+++ b/src/applications/phid/resolver/PhabricatorUserPHIDResolver.php
@@ -0,0 +1,27 @@
+<?php
+
+final class PhabricatorUserPHIDResolver
+  extends PhabricatorPHIDResolver {
+
+  protected function getResolutionMap(array $names) {
+    // Pick up the normalization and case rules from the PHID type query.
+
+    foreach ($names as $key => $name) {
+      $names[$key] = '@'.$name;
+    }
+
+    $query = id(new PhabricatorObjectQuery())
+      ->setViewer($this->getViewer());
+
+    $users = id(new PhabricatorPeopleUserPHIDType())
+      ->loadNamedObjects($query, $names);
+
+    $results = array();
+    foreach ($users as $at_username => $user) {
+      $results[substr($at_username, 1)] = $user->getPHID();
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/transactions/editengine/PhabricatorApplicationEditEngine.php b/src/applications/transactions/editengine/PhabricatorApplicationEditEngine.php
--- a/src/applications/transactions/editengine/PhabricatorApplicationEditEngine.php
+++ b/src/applications/transactions/editengine/PhabricatorApplicationEditEngine.php
@@ -146,14 +146,11 @@
           $project_phids = array();
         }
 
-        $edge_field = id(new PhabricatorDatasourceEditField())
+        $edge_field = id(new PhabricatorProjectsEditField())
           ->setKey('projectPHIDs')
           ->setLabel(pht('Projects'))
           ->setEditTypeKey('projects')
-          ->setDescription(
-            pht(
-              'Add or remove associated projects.'))
-          ->setDatasource(new PhabricatorProjectDatasource())
+          ->setDescription(pht('Add or remove associated projects.'))
           ->setAliases(array('project', 'projects'))
           ->setTransactionType($edge_type)
           ->setMetadataValue('edge:type', $project_edge_type)
@@ -175,12 +172,11 @@
           $sub_phids = array();
         }
 
-        $subscribers_field = id(new PhabricatorDatasourceEditField())
+        $subscribers_field = id(new PhabricatorSubscribersEditField())
           ->setKey('subscriberPHIDs')
           ->setLabel(pht('Subscribers'))
           ->setEditTypeKey('subscribers')
           ->setDescription(pht('Manage subscribers.'))
-          ->setDatasource(new PhabricatorMetaMTAMailableDatasource())
           ->setAliases(array('subscriber', 'subscribers'))
           ->setTransactionType($subscribers_type)
           ->setValue($sub_phids);
diff --git a/src/applications/transactions/editfield/PhabricatorProjectsEditField.php b/src/applications/transactions/editfield/PhabricatorProjectsEditField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/editfield/PhabricatorProjectsEditField.php
@@ -0,0 +1,14 @@
+<?php
+
+final class PhabricatorProjectsEditField
+  extends PhabricatorTokenizerEditField {
+
+  protected function newDatasource() {
+    return new PhabricatorProjectDatasource();
+  }
+
+  protected function newHTTPParameterType() {
+    return new AphrontProjectListHTTPParameterType();
+  }
+
+}
diff --git a/src/applications/transactions/editfield/PhabricatorSubscribersEditField.php b/src/applications/transactions/editfield/PhabricatorSubscribersEditField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/editfield/PhabricatorSubscribersEditField.php
@@ -0,0 +1,16 @@
+<?php
+
+final class PhabricatorSubscribersEditField
+  extends PhabricatorTokenizerEditField {
+
+  protected function newDatasource() {
+    return new PhabricatorMetaMTAMailableDatasource();
+  }
+
+  protected function newHTTPParameterType() {
+    // TODO: Implement a more expansive "Mailable" parameter type which
+    // accepts users or projects.
+    return new AphrontUserListHTTPParameterType();
+  }
+
+}
diff --git a/src/applications/transactions/editfield/PhabricatorUsersEditField.php b/src/applications/transactions/editfield/PhabricatorUsersEditField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/editfield/PhabricatorUsersEditField.php
@@ -0,0 +1,14 @@
+<?php
+
+final class PhabricatorUsersEditField
+  extends PhabricatorTokenizerEditField {
+
+  protected function newDatasource() {
+    return new PhabricatorPeopleDatasource();
+  }
+
+  protected function newHTTPParameterType() {
+    return new AphrontUserListHTTPParameterType();
+  }
+
+}