diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 3716d1ba9e..87463605d9 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -687,6 +687,9 @@ phutil_register_library_map(array(
     'HarbormasterPlanViewController' => 'applications/harbormaster/controller/HarbormasterPlanViewController.php',
     'HarbormasterRemarkupRule' => 'applications/harbormaster/remarkup/HarbormasterRemarkupRule.php',
     'HarbormasterScratchTable' => 'applications/harbormaster/storage/HarbormasterScratchTable.php',
+    'HarbormasterStepAddController' => 'applications/harbormaster/controller/HarbormasterStepAddController.php',
+    'HarbormasterStepDeleteController' => 'applications/harbormaster/controller/HarbormasterStepDeleteController.php',
+    'HarbormasterStepEditController' => 'applications/harbormaster/controller/HarbormasterStepEditController.php',
     'HeraldAction' => 'applications/herald/storage/HeraldAction.php',
     'HeraldAdapter' => 'applications/herald/adapter/HeraldAdapter.php',
     'HeraldApplyTranscript' => 'applications/herald/storage/transcript/HeraldApplyTranscript.php',
@@ -2919,6 +2922,9 @@ phutil_register_library_map(array(
     'HarbormasterPlanViewController' => 'HarbormasterPlanController',
     'HarbormasterRemarkupRule' => 'PhabricatorRemarkupRuleObject',
     'HarbormasterScratchTable' => 'HarbormasterDAO',
+    'HarbormasterStepAddController' => 'HarbormasterController',
+    'HarbormasterStepDeleteController' => 'HarbormasterController',
+    'HarbormasterStepEditController' => 'HarbormasterController',
     'HeraldAction' => 'HeraldDAO',
     'HeraldApplyTranscript' => 'HeraldDAO',
     'HeraldCapabilityManageGlobalRules' => 'PhabricatorPolicyCapability',
diff --git a/src/applications/harbormaster/application/PhabricatorApplicationHarbormaster.php b/src/applications/harbormaster/application/PhabricatorApplicationHarbormaster.php
index 6bcb87d7b1..bf0d7c21ac 100644
--- a/src/applications/harbormaster/application/PhabricatorApplicationHarbormaster.php
+++ b/src/applications/harbormaster/application/PhabricatorApplicationHarbormaster.php
@@ -46,6 +46,11 @@ final class PhabricatorApplicationHarbormaster extends PhabricatorApplication {
           'edit/(?:(?P<id>\d+)/)?' => 'HarbormasterBuildableEditController',
           'apply/(?:(?P<id>\d+)/)?' => 'HarbormasterBuildableApplyController',
         ),
+        'step/' => array(
+          'add/(?:(?P<id>\d+)/)?' => 'HarbormasterStepAddController',
+          'edit/(?:(?P<id>\d+)/)?' => 'HarbormasterStepEditController',
+          'delete/(?:(?P<id>\d+)/)?' => 'HarbormasterStepDeleteController',
+        ),
         'plan/' => array(
           '(?:query/(?P<queryKey>[^/]+)/)?'
             => 'HarbormasterPlanListController',
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildableViewController.php b/src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
index afe43b1423..a5c9c0b34d 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
@@ -62,6 +62,10 @@ final class HarbormasterBuildableViewController
           $item->setBarColor('red');
           $item->addAttribute(pht('Failed'));
           break;
+        case HarbormasterBuild::STATUS_ERROR:
+          $item->setBarColor('red');
+          $item->addAttribute(pht('Unexpected Error'));
+          break;
       }
       $build_list->addItem($item);
     }
diff --git a/src/applications/harbormaster/controller/HarbormasterPlanViewController.php b/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
index 58eefbe4ab..9cc6944202 100644
--- a/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
@@ -55,10 +55,13 @@ final class HarbormasterPlanViewController
       id(new PhabricatorCrumbView())
         ->setName(pht("Plan %d", $id)));
 
+    $step_list = $this->buildStepList($plan);
+
     return $this->buildApplicationPage(
       array(
         $crumbs,
         $box,
+        $step_list,
         $xaction_view,
       ),
       array(
@@ -67,6 +70,56 @@ final class HarbormasterPlanViewController
       ));
   }
 
+  private function buildStepList(HarbormasterBuildPlan $plan) {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $steps = id(new HarbormasterBuildStepQuery())
+      ->setViewer($viewer)
+      ->withBuildPlanPHIDs(array($plan->getPHID()))
+      ->execute();
+
+    $can_edit = $this->hasApplicationCapability(
+      HarbormasterCapabilityManagePlans::CAPABILITY);
+
+    $i = 1;
+    $step_list = id(new PHUIObjectItemListView())
+      ->setUser($viewer);
+    foreach ($steps as $step) {
+      $implementation = $step->getStepImplementation();
+      $item = id(new PHUIObjectItemView())
+        ->setObjectName("Step ".$i++)
+        ->setHeader($implementation->getName());
+
+      if (!$implementation->validateSettings()) {
+        $item
+          ->setBarColor('red')
+          ->addAttribute(pht('This step is not configured correctly.'));
+      } else {
+        $item->addAttribute($implementation->getDescription());
+      }
+
+      if ($can_edit) {
+        $edit_uri = $this->getApplicationURI("step/edit/".$step->getID()."/");
+        $item
+          ->setHref($edit_uri)
+          ->addAction(
+            id(new PHUIListItemView())
+              ->setIcon('delete')
+              ->addSigil('harbormaster-build-step-delete')
+              ->setWorkflow(true)
+              ->setRenderNameAsTooltip(true)
+              ->setName(pht("Delete"))
+              ->setHref(
+                $this->getApplicationURI("step/delete/".$step->getID()."/")));
+      }
+
+      $step_list->addItem($item);
+    }
+
+    return $step_list;
+  }
+
   private function buildActionList(HarbormasterBuildPlan $plan) {
     $request = $this->getRequest();
     $viewer = $request->getUser();
@@ -88,6 +141,14 @@ final class HarbormasterPlanViewController
         ->setDisabled(!$can_edit)
         ->setIcon('edit'));
 
+    $list->addAction(
+      id(new PhabricatorActionView())
+        ->setName(pht('Add Build Step'))
+        ->setHref($this->getApplicationURI("step/add/{$id}/"))
+        ->setWorkflow($can_edit)
+        ->setDisabled(!$can_edit)
+        ->setIcon('new'));
+
     return $list;
   }
 
diff --git a/src/applications/harbormaster/controller/HarbormasterStepAddController.php b/src/applications/harbormaster/controller/HarbormasterStepAddController.php
new file mode 100644
index 0000000000..095f6149ff
--- /dev/null
+++ b/src/applications/harbormaster/controller/HarbormasterStepAddController.php
@@ -0,0 +1,84 @@
+<?php
+
+final class HarbormasterStepAddController
+  extends HarbormasterController {
+
+  private $id;
+
+  public function willProcessRequest(array $data) {
+    $this->id = $data['id'];
+  }
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $this->requireApplicationCapability(
+      HarbormasterCapabilityManagePlans::CAPABILITY);
+
+    $id = $this->id;
+
+    $plan = id(new HarbormasterBuildPlanQuery())
+        ->setViewer($viewer)
+        ->withIDs(array($id))
+        ->executeOne();
+    if ($plan === null) {
+      throw new Exception("Build plan not found!");
+    }
+
+    $implementations = BuildStepImplementation::getImplementations();
+
+    $cancel_uri = $this->getApplicationURI('plan/'.$plan->getID().'/');
+
+    if ($request->isDialogFormPost()) {
+      $class = $request->getStr('step-type');
+      if (!in_array($class, $implementations)) {
+        return $this->createDialog($implementations);
+      }
+
+      $step = new HarbormasterBuildStep();
+      $step->setBuildPlanPHID($plan->getPHID());
+      $step->setClassName($class);
+      $step->setDetails(array());
+      $step->save();
+
+      $edit_uri = $this->getApplicationURI("step/edit/".$step->getID()."/");
+
+      return id(new AphrontRedirectResponse())->setURI($edit_uri);
+    }
+
+    return $this->createDialog($implementations, $cancel_uri);
+  }
+
+  function createDialog(array $implementations, $cancel_uri) {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $control = id(new AphrontFormRadioButtonControl())
+      ->setName('step-type');
+
+    foreach ($implementations as $implementation_name) {
+      $implementation = new $implementation_name();
+      $control
+        ->addButton(
+          $implementation_name,
+          $implementation->getName(),
+          $implementation->getGenericDescription());
+    }
+
+    $dialog = new AphrontDialogView();
+    $dialog->setTitle(pht('Add New Step'))
+            ->setUser($viewer)
+            ->addSubmitButton(pht('Add Build Step'))
+            ->addCancelButton($cancel_uri);
+    $dialog->appendChild(
+      phutil_tag(
+        'p',
+        array(),
+        pht(
+          'Select what type of build step you want to add: ')));
+    $dialog->appendChild($control);
+    return id(new AphrontDialogResponse())->setDialog($dialog);
+  }
+
+}
diff --git a/src/applications/harbormaster/controller/HarbormasterStepDeleteController.php b/src/applications/harbormaster/controller/HarbormasterStepDeleteController.php
new file mode 100644
index 0000000000..a11d565ba9
--- /dev/null
+++ b/src/applications/harbormaster/controller/HarbormasterStepDeleteController.php
@@ -0,0 +1,52 @@
+<?php
+
+final class HarbormasterStepDeleteController
+  extends HarbormasterController {
+
+  private $id;
+
+  public function willProcessRequest(array $data) {
+    $this->id = $data['id'];
+  }
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $this->requireApplicationCapability(
+      HarbormasterCapabilityManagePlans::CAPABILITY);
+
+    $id = $this->id;
+
+    $step = id(new HarbormasterBuildStepQuery())
+      ->setViewer($viewer)
+      ->withIDs(array($id))
+      ->executeOne();
+    if ($step === null) {
+      throw new Exception("Build step not found!");
+    }
+
+    $plan_id = $step->getBuildPlan()->getID();
+    $done_uri = $this->getApplicationURI('plan/'.$plan_id.'/');
+
+    if ($request->isDialogFormPost()) {
+      $step->delete();
+      return id(new AphrontRedirectResponse())->setURI($done_uri);
+    }
+
+    $dialog = new AphrontDialogView();
+    $dialog->setTitle(pht('Really Delete Step?'))
+            ->setUser($viewer)
+            ->addSubmitButton(pht('Delete Build Step'))
+            ->addCancelButton($done_uri);
+    $dialog->appendChild(
+      phutil_tag(
+        'p',
+        array(),
+        pht(
+          'Are you sure you want to delete this '.
+          'step? This can\'t be undone!')));
+    return id(new AphrontDialogResponse())->setDialog($dialog);
+  }
+
+}
diff --git a/src/applications/harbormaster/controller/HarbormasterStepEditController.php b/src/applications/harbormaster/controller/HarbormasterStepEditController.php
new file mode 100644
index 0000000000..81d3f0b2a8
--- /dev/null
+++ b/src/applications/harbormaster/controller/HarbormasterStepEditController.php
@@ -0,0 +1,156 @@
+<?php
+
+final class HarbormasterStepEditController
+  extends HarbormasterController {
+
+  private $id;
+
+  public function willProcessRequest(array $data) {
+    $this->id = idx($data, 'id');
+  }
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $this->requireApplicationCapability(
+      HarbormasterCapabilityManagePlans::CAPABILITY);
+
+    $step = id(new HarbormasterBuildStepQuery())
+      ->setViewer($viewer)
+      ->withIDs(array($this->id))
+      ->executeOne();
+    if (!$step) {
+      return new Aphront404Response();
+    }
+
+    $plan = id(new HarbormasterBuildPlanQuery())
+      ->setViewer($viewer)
+      ->withPHIDs(array($step->getBuildPlanPHID()))
+      ->executeOne();
+    if (!$plan) {
+      return new Aphront404Response();
+    }
+
+    $implementation = $step->getStepImplementation();
+    $implementation->validateSettingDefinitions();
+    $settings = $implementation->getSettings();
+
+    $errors = array();
+    if ($request->isFormPost()) {
+      foreach ($implementation->getSettingDefinitions() as $name => $opt) {
+        $readable_name = $this->getReadableName($name, $opt);
+        $value = $this->getValueFromRequest($request, $name, $opt['type']);
+
+        // TODO: This won't catch any validation issues unless the field
+        // is missing completely.  How should we check if the user is
+        // required to enter an integer?
+        if ($value === null) {
+          $errors[] = $readable_name.' is not valid.';
+        } else {
+          $step->setDetail($name, $value);
+        }
+      }
+
+      if (count($errors) === 0) {
+        $step->save();
+
+        return id(new AphrontRedirectResponse())
+          ->setURI($this->getApplicationURI('plan/'.$plan->getID().'/'));
+      }
+    }
+
+    $form = id(new AphrontFormView())
+      ->setUser($viewer);
+
+    // We need to render out all of the fields for the settings that
+    // the implementation has.
+    foreach ($implementation->getSettingDefinitions() as $name => $opt) {
+      if ($request->isFormPost()) {
+        $value = $this->getValueFromRequest($request, $name, $opt['type']);
+      } else {
+        $value = $settings[$name];
+      }
+
+      switch ($opt['type']) {
+        case BuildStepImplementation::SETTING_TYPE_STRING:
+        case BuildStepImplementation::SETTING_TYPE_INTEGER:
+          $control = id(new AphrontFormTextControl())
+            ->setLabel($this->getReadableName($name, $opt))
+            ->setName($name)
+            ->setValue($value);
+          break;
+        case BuildStepImplementation::SETTING_TYPE_BOOLEAN:
+          $control = id(new AphrontFormCheckboxControl())
+            ->setLabel($this->getReadableName($name, $opt))
+            ->setName($name)
+            ->setValue($value);
+          break;
+        default:
+          throw new Exception("Unable to render field with unknown type.");
+      }
+
+      if (isset($opt['description'])) {
+        $control->setCaption($opt['description']);
+      }
+
+      $form->appendChild($control);
+    }
+
+    $form->appendChild(
+      id(new AphrontFormSubmitControl())
+        ->setValue(pht('Save Step Configuration'))
+        ->addCancelButton(
+          $this->getApplicationURI('plan/'.$plan->getID().'/')));
+
+    $box = id(new PHUIObjectBoxView())
+      ->setHeaderText('Edit Step: '.$implementation->getName())
+      ->setValidationException(null)
+      ->setForm($form);
+
+    $crumbs = $this->buildApplicationCrumbs();
+    $id = $plan->getID();
+    $crumbs->addCrumb(
+      id(new PhabricatorCrumbView())
+        ->setName(pht("Plan %d", $id))
+        ->setHref($this->getApplicationURI("plan/{$id}/")));
+    $crumbs->addCrumb(
+      id(new PhabricatorCrumbView())
+        ->setName(pht('Edit Step')));
+
+    return $this->buildApplicationPage(
+      array(
+        $crumbs,
+        $box,
+      ),
+      array(
+        'title' => $implementation->getName(),
+        'device' => true,
+      ));
+  }
+
+  public function getReadableName($name, $opt) {
+    $readable_name = $name;
+    if (isset($opt['name'])) {
+      $readable_name = $opt['name'];
+    }
+    return $readable_name;
+  }
+
+  public function getValueFromRequest(AphrontRequest $request, $name, $type) {
+    switch ($type) {
+      case BuildStepImplementation::SETTING_TYPE_STRING:
+        return $request->getStr($name);
+        break;
+      case BuildStepImplementation::SETTING_TYPE_INTEGER:
+        return $request->getInt($name);
+        break;
+      case BuildStepImplementation::SETTING_TYPE_BOOLEAN:
+        return $request->getBool($name);
+        break;
+      default:
+        throw new Exception("Unsupported setting type '".$type."'.");
+    }
+  }
+
+}
diff --git a/src/applications/harbormaster/query/HarbormasterBuildStepQuery.php b/src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
index 61190b3285..3bcc057f16 100644
--- a/src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
+++ b/src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
@@ -22,6 +22,14 @@ final class HarbormasterBuildStepQuery
     return $this;
   }
 
+  public function getPagingColumn() {
+    return 'id';
+  }
+
+  public function getReversePaging() {
+    return true;
+  }
+
   protected function loadPage() {
     $table = new HarbormasterBuildStep();
     $conn_r = $table->establishConnection('r');
diff --git a/src/applications/harbormaster/step/BuildStepImplementation.php b/src/applications/harbormaster/step/BuildStepImplementation.php
index b782496a6f..6a524f4e39 100644
--- a/src/applications/harbormaster/step/BuildStepImplementation.php
+++ b/src/applications/harbormaster/step/BuildStepImplementation.php
@@ -4,13 +4,32 @@ abstract class BuildStepImplementation {
 
   private $settings;
 
+  const SETTING_TYPE_STRING = 'string';
+  const SETTING_TYPE_INTEGER = 'integer';
+  const SETTING_TYPE_BOOLEAN = 'boolean';
+
+  public static function getImplementations() {
+    $symbols = id(new PhutilSymbolLoader())
+      ->setAncestorClass("BuildStepImplementation")
+      ->setConcreteOnly(true)
+      ->selectAndLoadSymbols();
+    return ipull($symbols, 'name');
+  }
+
   /**
    * The name of the implementation.
    */
   abstract public function getName();
 
   /**
-   * The description of the implementation.
+   * The generic description of the implementation.
+   */
+  public function getGenericDescription() {
+    return '';
+  }
+
+  /**
+   * The description of the implementation, based on the current settings.
    */
   public function getDescription() {
     return '';
@@ -24,21 +43,42 @@ abstract class BuildStepImplementation {
   /**
    * Gets the settings for this build step.
    */
-  protected function getSettings() {
+  public function getSettings() {
     return $this->settings;
   }
 
+  /**
+   * Validate the current settings of this build step.
+   */
+  public function validate() {
+    return true;
+  }
+
   /**
    * Loads the settings for this build step implementation from the build step.
    */
   public final function loadSettings(HarbormasterBuildStep $build_step) {
     $this->settings = array();
+    $this->validateSettingDefinitions();
     foreach ($this->getSettingDefinitions() as $name => $opt) {
       $this->settings[$name] = $build_step->getDetail($name);
     }
     return $this->settings;
   }
 
+  /**
+   * Validates that the setting definitions for this implementation are valid.
+   */
+  public final function validateSettingDefinitions() {
+    foreach ($this->getSettingDefinitions() as $name => $opt) {
+      if (!isset($opt['type'])) {
+        throw new Exception(
+          'Setting definition \''.$name.
+          '\' is missing type requirement.');
+      }
+    }
+  }
+
   /**
    * Return an array of settings for this step implementation.
    */
diff --git a/src/applications/harbormaster/step/SleepBuildStepImplementation.php b/src/applications/harbormaster/step/SleepBuildStepImplementation.php
index bf16b22d23..e80f559e29 100644
--- a/src/applications/harbormaster/step/SleepBuildStepImplementation.php
+++ b/src/applications/harbormaster/step/SleepBuildStepImplementation.php
@@ -6,19 +6,40 @@ final class SleepBuildStepImplementation extends BuildStepImplementation {
     return pht('Sleep');
   }
 
-  public function getDescription() {
+  public function getGenericDescription() {
     return pht('Sleep for a specified number of seconds.');
   }
 
+  public function getDescription() {
+    $settings = $this->getSettings();
+
+    return pht('Sleep for %s seconds.', $settings['seconds']);
+  }
+
   public function execute(HarbormasterBuild $build) {
     $settings = $this->getSettings();
 
     sleep($settings['seconds']);
   }
 
+  public function validateSettings() {
+    $settings = $this->getSettings();
+
+    if ($settings['seconds'] === null) {
+      return false;
+    }
+    if (!is_int($settings['seconds'])) {
+      return false;
+    }
+    return true;
+  }
+
   public function getSettingDefinitions() {
     return array(
-      'seconds' => array());
+      'seconds' => array(
+        'name' => 'Seconds',
+        'description' => 'The number of seconds to sleep for.',
+        'type' => BuildStepImplementation::SETTING_TYPE_INTEGER));
   }
 
 }
diff --git a/src/applications/harbormaster/storage/build/HarbormasterBuild.php b/src/applications/harbormaster/storage/build/HarbormasterBuild.php
index c7d5aa7181..aa8e6c4f53 100644
--- a/src/applications/harbormaster/storage/build/HarbormasterBuild.php
+++ b/src/applications/harbormaster/storage/build/HarbormasterBuild.php
@@ -40,6 +40,11 @@ final class HarbormasterBuild extends HarbormasterDAO
    */
   const STATUS_FAILED = 'failed';
 
+  /**
+   * The build encountered an unexpected error.
+   */
+  const STATUS_ERROR = 'error';
+
   public static function initializeNewBuild(PhabricatorUser $actor) {
     return id(new HarbormasterBuild())
       ->setBuildStatus(self::STATUS_INACTIVE);
diff --git a/src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php b/src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
index 42a7e89fa9..cb9310d2aa 100644
--- a/src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
+++ b/src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
@@ -46,9 +46,16 @@ final class HarbormasterBuildStep extends HarbormasterDAO
       throw new Exception("No implementation set for the given step.");
     }
 
-    // TODO: We should look up the class in phutil's system to ensure
-    // that it actually extends BuildStepImplementation.
+    static $implementations = null;
+    if ($implementations === null) {
+      $implementations = BuildStepImplementation::getImplementations();
+    }
+
     $class = $this->className;
+    if (!in_array($class, $implementations)) {
+      throw new Exception(
+        "Class name '".$class."' does not extend BuildStepImplementation.");
+    }
     $implementation = newv($class, array());
     $implementation->loadSettings($this);
     return $implementation;
diff --git a/src/applications/harbormaster/worker/HarbormasterBuildWorker.php b/src/applications/harbormaster/worker/HarbormasterBuildWorker.php
index 347119e348..0306c18d8f 100644
--- a/src/applications/harbormaster/worker/HarbormasterBuildWorker.php
+++ b/src/applications/harbormaster/worker/HarbormasterBuildWorker.php
@@ -40,6 +40,10 @@ final class HarbormasterBuildWorker extends PhabricatorWorker {
       // Perform the build.
       foreach ($steps as $step) {
         $implementation = $step->getStepImplementation();
+        if (!$implementation->validateSettings()) {
+          $build->setBuildStatus(HarbormasterBuild::STATUS_ERROR);
+          break;
+        }
         $implementation->execute($build);
         if ($build->getBuildStatus() !== HarbormasterBuild::STATUS_BUILDING) {
           break;
@@ -56,7 +60,7 @@ final class HarbormasterBuildWorker extends PhabricatorWorker {
       // If any exception is raised, the build is marked as a failure and
       // the exception is re-thrown (this ensures we don't leave builds
       // in an inconsistent state).
-      $build->setBuildStatus(HarbormasterBuild::STATUS_FAILED);
+      $build->setBuildStatus(HarbormasterBuild::STATUS_ERROR);
       $build->save();
       throw $e;
     }