diff --git a/resources/sql/autopatches/20141006.phortunecart.sql b/resources/sql/autopatches/20141006.phortunecart.sql
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20141006.phortunecart.sql
@@ -0,0 +1,4 @@
+TRUNCATE TABLE {$NAMESPACE}_phortune.phortune_cart;
+
+ALTER TABLE {$NAMESPACE}_phortune.phortune_cart
+  ADD cartClass VARCHAR(128) NOT NULL COLLATE utf8_bin;
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
@@ -666,6 +666,7 @@
     'FlagEditConduitAPIMethod' => 'applications/flag/conduit/FlagEditConduitAPIMethod.php',
     'FlagQueryConduitAPIMethod' => 'applications/flag/conduit/FlagQueryConduitAPIMethod.php',
     'FundBacker' => 'applications/fund/storage/FundBacker.php',
+    'FundBackerCart' => 'applications/fund/phortune/FundBackerCart.php',
     'FundBackerEditor' => 'applications/fund/editor/FundBackerEditor.php',
     'FundBackerListController' => 'applications/fund/controller/FundBackerListController.php',
     'FundBackerPHIDType' => 'applications/fund/phid/FundBackerPHIDType.php',
@@ -2555,6 +2556,7 @@
     'PhortuneCart' => 'applications/phortune/storage/PhortuneCart.php',
     'PhortuneCartCheckoutController' => 'applications/phortune/controller/PhortuneCartCheckoutController.php',
     'PhortuneCartController' => 'applications/phortune/controller/PhortuneCartController.php',
+    'PhortuneCartImplementation' => 'applications/phortune/cart/PhortuneCartImplementation.php',
     'PhortuneCartQuery' => 'applications/phortune/query/PhortuneCartQuery.php',
     'PhortuneCartViewController' => 'applications/phortune/controller/PhortuneCartViewController.php',
     'PhortuneCharge' => 'applications/phortune/storage/PhortuneCharge.php',
@@ -3514,6 +3516,7 @@
       'PhabricatorPolicyInterface',
       'PhabricatorApplicationTransactionInterface',
     ),
+    'FundBackerCart' => 'PhortuneCartImplementation',
     'FundBackerEditor' => 'PhabricatorApplicationTransactionEditor',
     'FundBackerListController' => 'FundController',
     'FundBackerPHIDType' => 'PhabricatorPHIDType',
diff --git a/src/applications/fund/controller/FundInitiativeBackController.php b/src/applications/fund/controller/FundInitiativeBackController.php
--- a/src/applications/fund/controller/FundInitiativeBackController.php
+++ b/src/applications/fund/controller/FundInitiativeBackController.php
@@ -70,7 +70,10 @@
           $viewer,
           PhabricatorContentSource::newFromRequest($request));
 
-        $cart = $account->newCart($viewer);
+        $cart_implementation = id(new FundBackerCart())
+          ->setInitiative($initiative);
+
+        $cart = $account->newCart($viewer, $cart_implementation);
 
         $purchase = $cart->newPurchase($viewer, $product);
         $purchase
diff --git a/src/applications/fund/phortune/FundBackerCart.php b/src/applications/fund/phortune/FundBackerCart.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fund/phortune/FundBackerCart.php
@@ -0,0 +1,80 @@
+<?php
+
+final class FundBackerCart extends PhortuneCartImplementation {
+
+  private $initiativePHID;
+  private $initiative;
+
+  public function setInitiativePHID($initiative_phid) {
+    $this->initiativePHID = $initiative_phid;
+    return $this;
+  }
+
+  public function getInitiativePHID() {
+    return $this->initiativePHID;
+  }
+
+  public function setInitiative(FundInitiative $initiative) {
+    $this->initiative = $initiative;
+    return $this;
+  }
+
+  public function getInitiative() {
+    return $this->initiative;
+  }
+
+  public function willCreateCart(
+    PhabricatorUser $viewer,
+    PhortuneCart $cart) {
+
+    $initiative = $this->getInitiative();
+    if (!$initiative) {
+      throw new Exception(
+        pht('Call setInitiative() before building a cart!'));
+    }
+
+    $cart->setMetadataValue('initiativePHID', $initiative->getPHID());
+  }
+
+  public function loadImplementationsForCarts(
+    PhabricatorUser $viewer,
+    array $carts) {
+
+    $phids = array();
+    foreach ($carts as $cart) {
+      $phids[] = $cart->getMetadataValue('initiativePHID');
+    }
+
+    $initiatives = id(new FundInitiativeQuery())
+      ->setViewer($viewer)
+      ->withPHIDs($phids)
+      ->execute();
+    $initiatives = mpull($initiatives, null, 'getPHID');
+
+    $objects = array();
+    foreach ($carts as $key => $cart) {
+      $initiative_phid = $cart->getMetadataValue('initiativePHID');
+
+      $object = id(new FundBackerCart())
+        ->setInitiativePHID($initiative_phid);
+
+      $initiative = idx($initiatives, $initiative_phid);
+      if ($initiative) {
+        $object->setInitiative($initiative);
+      }
+
+      $objects[$key] = $object;
+    }
+
+    return $objects;
+  }
+
+  public function getCancelURI(PhortuneCart $cart) {
+    return '/'.$this->getInitiative()->getMonogram();
+  }
+
+  public function getDoneURI(PhortuneCart $cart) {
+    return '/'.$this->getInitiative()->getMonogram();
+  }
+
+}
diff --git a/src/applications/phortune/cart/PhortuneCartImplementation.php b/src/applications/phortune/cart/PhortuneCartImplementation.php
new file mode 100644
--- /dev/null
+++ b/src/applications/phortune/cart/PhortuneCartImplementation.php
@@ -0,0 +1,22 @@
+<?php
+
+abstract class PhortuneCartImplementation {
+
+  /**
+   * Load implementations for a given set of carts.
+   *
+   * Note that this method should return a map using the original keys to
+   * identify which implementation corresponds to which cart.
+   */
+  abstract public function loadImplementationsForCarts(
+    PhabricatorUser $viewer,
+    array $carts);
+
+  abstract public function getCancelURI(PhortuneCart $cart);
+  abstract public function getDoneURI(PhortuneCart $cart);
+
+  abstract public function willCreateCart(
+    PhabricatorUser $viewer,
+    PhortuneCart $cart);
+
+}
diff --git a/src/applications/phortune/controller/PhortuneCartCheckoutController.php b/src/applications/phortune/controller/PhortuneCartCheckoutController.php
--- a/src/applications/phortune/controller/PhortuneCartCheckoutController.php
+++ b/src/applications/phortune/controller/PhortuneCartCheckoutController.php
@@ -162,11 +162,15 @@
     }
 
     if ($methods || $add_providers) {
-      $form
-        ->appendChild(
-          id(new AphrontFormSubmitControl())
-            ->setValue(pht('Submit Payment'))
-            ->setDisabled(!$methods));
+      $submit = id(new AphrontFormSubmitControl())
+        ->setValue(pht('Submit Payment'))
+        ->setDisabled(!$methods);
+
+      if ($cart->getCancelURI() !== null) {
+        $submit->addCancelButton($cart->getCancelURI());
+      }
+
+      $form->appendChild($submit);
     }
 
     $provider_form = null;
diff --git a/src/applications/phortune/query/PhortuneCartQuery.php b/src/applications/phortune/query/PhortuneCartQuery.php
--- a/src/applications/phortune/query/PhortuneCartQuery.php
+++ b/src/applications/phortune/query/PhortuneCartQuery.php
@@ -66,6 +66,24 @@
       $cart->attachAccount($account);
     }
 
+    $implementations = array();
+
+    $cart_map = mgroup($carts, 'getCartClass');
+    foreach ($cart_map as $class => $class_carts) {
+      $implementations += newv($class, array())->loadImplementationsForCarts(
+        $this->getViewer(),
+        $class_carts);
+    }
+
+    foreach ($carts as $key => $cart) {
+      $implementation = idx($implementations, $key);
+      if (!$implementation) {
+        unset($carts[$key]);
+        continue;
+      }
+      $cart->attachImplementation($implementation);
+    }
+
     return $carts;
   }
 
diff --git a/src/applications/phortune/storage/PhortuneAccount.php b/src/applications/phortune/storage/PhortuneAccount.php
--- a/src/applications/phortune/storage/PhortuneAccount.php
+++ b/src/applications/phortune/storage/PhortuneAccount.php
@@ -56,9 +56,18 @@
     return $account;
   }
 
-  public function newCart(PhabricatorUser $actor) {
-    return PhortuneCart::initializeNewCart($actor, $this)
-      ->save();
+  public function newCart(
+    PhabricatorUser $actor,
+    PhortuneCartImplementation $implementation) {
+
+    $cart = PhortuneCart::initializeNewCart($actor, $this);
+
+    $cart->setCartClass(get_class($implementation));
+    $cart->attachImplementation($implementation);
+
+    $implementation->willCreateCart($actor, $cart);
+
+    return $cart->save();
   }
 
   public function getConfiguration() {
diff --git a/src/applications/phortune/storage/PhortuneCart.php b/src/applications/phortune/storage/PhortuneCart.php
--- a/src/applications/phortune/storage/PhortuneCart.php
+++ b/src/applications/phortune/storage/PhortuneCart.php
@@ -11,11 +11,13 @@
 
   protected $accountPHID;
   protected $authorPHID;
+  protected $cartClass;
   protected $status;
-  protected $metadata;
+  protected $metadata = array();
 
   private $account = self::ATTACHABLE;
   private $purchases = self::ATTACHABLE;
+  private $implementation = self::ATTACHABLE;
 
   public static function initializeNewCart(
     PhabricatorUser $actor,
@@ -73,13 +75,11 @@
 
 
   public function getDoneURI() {
-    // TODO: Implement properly.
-    return '/phortune/cart/'.$this->getID().'/';
+    return $this->getImplementation()->getDoneURI($this);
   }
 
   public function getCancelURI() {
-    // TODO: Implement properly.
-    return '/';
+    return $this->getImplementation()->getCancelURI($this);
   }
 
   public function getDetailURI() {
@@ -98,6 +98,7 @@
       ),
       self::CONFIG_COLUMN_SCHEMA => array(
         'status' => 'text32',
+        'cartClass' => 'text128',
       ),
       self::CONFIG_KEY_SCHEMA => array(
         'key_account' => array(
@@ -131,6 +132,16 @@
     return $this->assertAttached($this->account);
   }
 
+  public function attachImplementation(
+    PhortuneCartImplementation $implementation) {
+    $this->implementation = $implementation;
+    return $this;
+  }
+
+  public function getImplementation() {
+    return $this->assertAttached($this->implementation);
+  }
+
   public function getTotalPriceAsCurrency() {
     $prices = array();
     foreach ($this->getPurchases() as $purchase) {
@@ -140,6 +151,15 @@
     return PhortuneCurrency::newFromList($prices);
   }
 
+  public function setMetadataValue($key, $value) {
+    $this->metadata[$key] = $value;
+    return $this;
+  }
+
+  public function getMetadataValue($key, $default = null) {
+    return idx($this->metadata, $key, $default);
+  }
+
 
 /* -(  PhabricatorPolicyInterface  )----------------------------------------- */