diff --git a/includes/admin.form.inc b/includes/admin.form.inc
index d34bd5d5..b0bb0642 100644
--- a/includes/admin.form.inc
+++ b/includes/admin.form.inc
@@ -55,6 +55,12 @@ function islandora_repository_admin(array $form, array &$form_state) {
           '#description' => t('The PID of the Root Collection Object'),
           '#required' => TRUE,
         ),
+        'islandora_use_datastream_cache_headers' => array(
+          '#type' => 'checkbox',
+          '#title' => t('Generate/parse datastream HTTP cache headers'),
+          '#description' => t('HTTP caching can reduce network traffic, by allowing clients to used cached copies.'),
+          '#default_value' => variable_get('islandora_use_datastream_cache_headers', TRUE),
+        ),
       ),
       'islandora_namespace' => array(
         '#type' => 'fieldset',
diff --git a/includes/breadcrumb.inc b/includes/breadcrumb.inc
index 872eb70a..05ab1bac 100644
--- a/includes/breadcrumb.inc
+++ b/includes/breadcrumb.inc
@@ -27,6 +27,8 @@
 function islandora_get_breadcrumbs($object) {
   $breadcrumbs = islandora_get_breadcrumbs_recursive($object->id, $object->repository);
   array_pop($breadcrumbs);
+  $context = 'islandora';
+  drupal_alter('islandora_breadcrumbs', $breadcrumbs, $context);
   return $breadcrumbs;
 }
 
diff --git a/includes/datastream.inc b/includes/datastream.inc
index 585fa2f5..1d506e3d 100644
--- a/includes/datastream.inc
+++ b/includes/datastream.inc
@@ -46,8 +46,6 @@ function islandora_view_datastream(AbstractDatastream $datastream, $download = F
     }
   }
 
-  header_remove('Cache-Control');
-  header_remove('Expires');
   header('Content-type: ' . $datastream->mimetype);
   if ($datastream->controlGroup == 'M' || $datastream->controlGroup == 'X') {
     header('Content-length: ' . $datastream->size);
@@ -59,13 +57,164 @@ function islandora_view_datastream(AbstractDatastream $datastream, $download = F
     $filename = $datastream->label . '.' . $extension;
     header("Content-Disposition: attachment; filename=\"$filename\"");
   }
+
+  $cache_check = islandora_view_datastream_cache_check($datastream);
+  if ($cache_check !== 200) {
+    if ($cache_check === 304) {
+      header('HTTP/1.1 304 Not Modified');
+    }
+    elseif ($cache_check === 412) {
+      header('HTTP/1.0 412 Precondition Failed');
+    }
+  }
+  islandora_view_datastream_set_cache_headers($datastream);
+
   drupal_page_is_cacheable(FALSE);
   // Try not to load the file into PHP memory!
-  ob_end_flush();
-  $datastream->getContent('php://output');
+  // Close and flush ALL the output buffers!
+  while (@ob_end_flush()) {
+  };
+
+  // New content needed.
+  if ($cache_check === 200) {
+    $datastream->getContent('php://output');
+  }
   exit();
 }
 
+/**
+ * Parse "etags" from HTTP If-Match or If-None-Match headers.
+ *
+ * Parses from the CSV-like struture supported by HTTP headers into an array,
+ * so `"asdf", "fdsa", W/"2132"` should become an array containing the strings:
+ * - asdf
+ * - fdsa
+ * - 2132
+ *
+ * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.24
+ * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
+ *
+ * @param string $header_value
+ *   The value from the headers.
+ *
+ * @return array
+ *   An array containing all the etags present.
+ */
+function islandora_parse_http_match_headers($header_value) {
+  $matches = array();
+  // Match the CSV-like structure supported by the HTTP headers.
+  $count = preg_match_all('/(((W\/)?("?)(\*|.+?)\4)(, +)?)/', $header_value, $matches);
+  // The fifth sub-expression/group is which will contain the etags.
+  return $matches[5];
+}
+
+/**
+ * Validate cache headers.
+ *
+ * @param AbstractDatastream $datastream
+ *   The datastream for which to check the request headers against.
+ *
+ * @return int
+ *   An integer representing the HTTP response code. One of:
+ *   - 200: Proceed as normal. (Full download).
+ *   - 304: Resource hasn't changed; pass cache validation.
+ *   - 412: Resource has changed; fail cache validation.
+ *
+ * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
+ */
+function islandora_view_datastream_cache_check(AbstractDatastream $datastream) {
+  if (!variable_get('islandora_use_datastream_cache_headers', TRUE)) {
+    return 200;
+  }
+
+  // Let's assume that if we get here, we'll be able to complete the request.
+  $return = 200;
+
+  if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
+    $modified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_MODIFIED_SINCE']);
+    if ($datastream->createdDate->getTimestamp() - $modified_since->getTimestamp() > 0) {
+      // Changed!
+      return $return;
+    }
+    else {
+      $return = 304;
+    }
+  }
+  if ($return === 200 && isset($_SERVER['HTTP_IF_UNMODIFIED_SINCE'])) {
+    $unmodified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_UNMODIFIED_SINCE']);
+    if ($datastream->createdDate->getTimestamp() !== $unmodified_since->getTimestamp()) {
+      // Changed!
+      $return = 412;
+    }
+    else {
+      return $return;
+    }
+  }
+
+  // Only consider Etags we have provided.
+  if (isset($datastream->checksum)) {
+    $tags = array();
+    foreach ($datastream as $offset => $version) {
+      if (isset($version->checksum)) {
+        $tags[$offset] = $version->checksum;
+      }
+    }
+
+    if ($return === 200 && isset($_SERVER['HTTP_IF_MATCH'])) {
+      $request_tags = islandora_parse_http_match_headers($_SERVER['HTTP_IF_MATCH']);
+      if (in_array('*', $request_tags) || count(array_intersect($tags, $request_tags)) > 0) {
+        // There's a match... Let things go ahead.
+        return $return;
+      }
+      else {
+        $return = 412;
+      }
+    }
+    if (in_array($return, array(200, 304), TRUE) && isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
+      $request_tags = islandora_parse_http_match_headers($_SERVER['HTTP_IF_NONE_MATCH']);
+      if (in_array('*', $request_tags) || count(array_intersect($tags, $request_tags)) > 0) {
+        $return = 304;
+      }
+      else {
+        $return = 200;
+      }
+    }
+  }
+
+  return $return;
+}
+
+/**
+ * Set various HTTP headers for caching.
+ *
+ * @param AbstractDatastream $datastream
+ *   The datastream being viewed/downloaded.
+ */
+function islandora_view_datastream_set_cache_headers(AbstractDatastream $datastream) {
+  if (variable_get('islandora_use_datastream_cache_headers', TRUE)) {
+    // Force cache revalidation.
+    header('Expires: Sun, 19 Nov 1978 05:00:00 GMT');
+    $cache_control = array();
+    if ($datastream->parent->repository->api->connection->username == 'anonymous') {
+      $cache_control[] = 'public';
+    }
+    else {
+      $cache_control[] = 'private';
+    }
+    $cache_control[] = 'must-revalidate';
+    $cache_control[] = 'max-age=0';
+    header('Cache-Control: ' . implode(', ', $cache_control));
+    header('Last-Modified: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'));
+    if (isset($datastream->checksum)) {
+      header("Etag: \"{$datastream->checksum}\"");
+    }
+  }
+  else {
+    header_remove('Cache-Control');
+    header_remove('Expires');
+  }
+}
+
 /**
  * Get the human readable size of the given datastream.
  *
diff --git a/includes/solution_packs.inc b/includes/solution_packs.inc
index a80c41a5..7cf0351a 100644
--- a/includes/solution_packs.inc
+++ b/includes/solution_packs.inc
@@ -745,7 +745,9 @@ function islandora_get_viewer($params = NULL, $variable_id = NULL, $fedora_objec
     $viewer_id = islandora_get_viewer_id($variable_id);
     if ($viewer_id AND $params !== NULL) {
       $callback = islandora_get_viewer_callback($viewer_id);
-      return $callback($params, $fedora_object);
+      if (function_exists($callback)) {
+        return $callback($params, $fedora_object);
+      }
     }
   }
   return FALSE;
diff --git a/islandora.api.php b/islandora.api.php
index 2e6ef831..39c6e454 100644
--- a/islandora.api.php
+++ b/islandora.api.php
@@ -86,7 +86,7 @@ function hook_CMODEL_PID_islandora_view_object_alter(&$object, &$rendered) {
 }
 
 /**
- * Generate an object's management display.
+ * Generate an object's datastreams management display.
  *
  * @param AbstractObject $object
  *   A Tuque FedoraObject
@@ -98,7 +98,7 @@ function hook_islandora_edit_object($object) {
 }
 
 /**
- * Generate an object's management display for the given content model.
+ * Generate an object's datastreams management display based on content model.
  *
  * Content models PIDs have colons and hyphens changed to underscores, to
  * create the hook name.
@@ -113,7 +113,7 @@ function hook_CMODEL_PID_islandora_edit_object($object) {
 }
 
 /**
- * Allow management display output to be altered.
+ * Allow datastreams management display output to be altered.
  *
  * @param AbstractObject $object
  *   A Tuque FedoraObject
@@ -650,6 +650,7 @@ function hook_CMODEL_PID_islandora_derivative() {
 }
 
 /**
+
  * Retrieves PIDS of related objects for property updating.
  *
  * @param AbstractObject $object
@@ -663,3 +664,14 @@ function hook_islandora_update_related_objects_properties(AbstractObject $object
   }
   return $pids_to_return;
 }
+/**
+ * Alters breadcrumbs used on Solr search results and within Islandora views.
+ *
+ * @param array $breadcrumbs
+ *   Breadcrumbs array to be altered by reference. Each element is markup.
+ * @param string $context
+ *   Where the alter is originating from for distinguishing.
+ */
+function hook_islandora_breadcrumbs_alter(&$breadcrumbs, $context) {
+
+}
diff --git a/islandora.info b/islandora.info
index 4b48bc29..36ed0dff 100644
--- a/islandora.info
+++ b/islandora.info
@@ -18,5 +18,6 @@ files[] = tests/ingest.test
 files[] = tests/hooked_access.test
 files[] = tests/islandora_manage_permissions.test
 files[] = tests/datastream_versions.test
+files[] = tests/datastream_cache.test
 files[] = tests/derivatives.test
 php = 5.3
diff --git a/islandora.module b/islandora.module
index a81de4ec..b02bdc61 100644
--- a/islandora.module
+++ b/islandora.module
@@ -122,12 +122,21 @@ function islandora_menu() {
     'access callback' => 'islandora_object_access_callback',
     'access arguments' => array(ISLANDORA_VIEW_OBJECTS, 2),
   );
-  $items['islandora/object/%islandora_object/print'] = array(
+  $items['islandora/object/%islandora_object/print_object'] = array(
     'page callback' => 'islandora_printer_object',
     'page arguments' => array(2),
     'type' => MENU_NORMAL_ITEM,
-    'access callback' => 'islandora_object_access_callback',
+    'access callback' => 'islandora_object_access',
+    'access arguments' => array(ISLANDORA_VIEW_OBJECTS, 2),
+  );
+  $items['islandora/object/%islandora_object/print'] = array(
+    'title' => 'Print Object',
+    'page callback' => 'islandora_print_object',
+    'page arguments' => array(2),
+    'type' => MENU_CALLBACK,
+    'access callback' => 'islandora_object_access',
     'access arguments' => array(ISLANDORA_VIEW_OBJECTS, 2),
+    'load arguments' => array(2),
   );
   $items['islandora/object/%islandora_object/view'] = array(
     'title' => 'View',
@@ -154,13 +163,11 @@ function islandora_menu() {
         ISLANDORA_INGEST,
       ), 2),
   );
-
   $items['islandora/object/%islandora_object/manage/overview'] = array(
     'title' => 'Overview',
     'type' => MENU_DEFAULT_LOCAL_TASK,
     'weight' => -20,
   );
-
   $items['islandora/object/%islandora_object/manage/datastreams'] = array(
     'title' => 'Datastreams',
     'type' => MENU_LOCAL_TASK,
@@ -175,7 +182,6 @@ function islandora_menu() {
       ), 2),
     'weight' => -10,
   );
-
   $items['islandora/object/%islandora_object/manage/properties'] = array(
     'title' => 'Properties',
     'page callback' => 'drupal_get_form',
@@ -374,8 +380,13 @@ function islandora_theme() {
       'file' => 'includes/solution_packs.inc',
       'render element' => 'form',
     ),
-    // Print object view.
+    // Print used by the clipper.
     'islandora_object_print' => array(
+      'file' => 'theme/theme.inc',
+      'variables' => array('object' => NULL, 'content' => array()),
+    ),
+    // Print object view, prints islandora objects.
+    'islandora_object_print_object' => array(
       'file' => 'theme/theme.inc',
       'template' => 'theme/islandora-object-print',
       'variables' => array(
@@ -477,6 +488,22 @@ function islandora_permission() {
   );
 }
 
+/**
+ * Renders the print page for the given object.
+ *
+ * Modules can either implement preprocess functions to append content onto the
+ * 'content' variable, or override the display by providing a theme suggestion.
+ *
+ * @param AbstractObject $object
+ *   The object.
+ *
+ * @return array
+ *   A renderable array.
+ */
+function islandora_print_object(AbstractObject $object) {
+  drupal_set_title($object->label);
+  return theme('islandora_object_print', array('object' => $object));
+}
 /**
  * Implements hook_forms().
  */
@@ -848,7 +875,12 @@ function islandora_view_object(AbstractObject $object) {
 
   drupal_add_js(array(
     'islandora' => array(
+<<<<<<< HEAD
       'print_link' => 'islandora/object/' . $object->id . '/print')), array('type' => 'setting'));
+=======
+      'print_link' => 'islandora/object/' . $object->id . '/print_object')),
+    array('type' => 'setting'));
+>>>>>>> dd50626677e1acbc5fe69daf25d13cfa65dae7af
   drupal_add_js($path . '/js/add_print.js');
 
   drupal_set_title($object->label);
@@ -977,7 +1009,7 @@ function islandora_default_islandora_printer_object($object, $alter) {
   }
 
   $variables = isset($dc_object) ? $dc_object->asArray() : array();
-  $output = theme('islandora_object_print', array(
+  $output = theme('islandora_object_print_object', array(
     'object' => $object,
     'dc_array' => $variables,
     'islandora_content' => $alter));
diff --git a/tests/datastream_cache.test b/tests/datastream_cache.test
new file mode 100644
index 00000000..8118c08a
--- /dev/null
+++ b/tests/datastream_cache.test
@@ -0,0 +1,160 @@
+<?php
+
+/**
+ * @file
+ * Tests to verify the cache headers we provide.
+ */
+
+class IslandoraDatastreamCacheTestCase extends IslandoraWebTestCase {
+
+  /**
+   * Gets info to display to describe this test.
+   *
+   * @see IslandoraWebTestCase::getInfo()
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'Datastream Cache Headers',
+      'description' => 'Check our headers work as we expect them to.',
+      'group' => 'Islandora',
+    );
+  }
+
+  /**
+   * Creates an admin user and a connection to a fedora repository.
+   *
+   * @see IslandoraWebTestCase::setUp()
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->repository = $this->admin->repository;
+    $this->purgeTestObjects();
+  }
+
+  /**
+   * Free any objects/resources created for this test.
+   *
+   * @see IslandoraWebTestCase::tearDown()
+   */
+  public function tearDown() {
+    $this->purgeTestObjects();
+    parent::tearDown();
+  }
+
+  /**
+   * Purge any objects created by the test's in this class.
+   */
+  public function purgeTestObjects() {
+    $objects = array(
+      'test:test',
+    );
+    foreach ($objects as $object) {
+      try {
+        $object = $this->repository->getObject($object);
+        $this->repository->purgeObject($object->id);
+      }
+      catch (Exception $e) {
+        // Meh... Either it didn't exist or the purge failed.
+      }
+    }
+  }
+
+  /**
+   * Create our test object.
+   */
+  protected function createTestObject() {
+    $object = $this->repository->constructObject('test:test');
+    $object->label = 'Test object';
+    $object->models = 'test:model';
+    $datastream = $object->constructDatastream('asdf', 'M');
+    $datastream->label = 'datastream of doom';
+    $datastream->mimetype = 'text/plain';
+    $datastream->content = 'And then things happened.';
+    $datastream->checksumType = 'SHA-1';
+    $object->ingestDatastream($datastream);
+    $this->repository->ingestObject($object);
+    return $object;
+  }
+
+  /**
+   * Test HTTP cache headers.
+   */
+  public function testCacheHeaders() {
+    $object = $this->createTestObject();
+    $datastream = $object['asdf'];
+
+    $user = $this->drupalCreateUser(array(ISLANDORA_VIEW_OBJECTS));
+    $this->drupalLogin($user);
+
+    // Test If-Modified-Since.
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Modified-Since: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'),
+    ));
+    $this->assertResponse(304);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Modified-Since: ' . $datastream->createdDate->sub(new DateInterval('P1M'))->format('D, d M Y H:i:s \G\M\T'),
+    ));
+    $this->assertResponse(200);
+
+    // Test If-Unmodified-Since.
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Unmodified-Since: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'),
+    ));
+    $this->assertResponse(200);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Unmodified-Since: ' . $datastream->createdDate->sub(new DateInterval('P1M'))->format('D, d M Y H:i:s \G\M\T'),
+    ));
+    $this->assertResponse(412);
+
+    // Test If-Match.
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      format_string('If-Match: "!checksum"', array(
+        '!checksum' => $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(200);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      format_string('If-Match: "!checksum"', array(
+        '!checksum' => 'dont-match' . $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(412);
+
+    // Test If-None-Match.
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      format_string('If-None-Match: "!checksum"', array(
+        '!checksum' => $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(304);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      format_string('If-None-Match: "!checksum"', array(
+        '!checksum' => 'dont-match' . $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(200);
+
+    // Test combination of If-None-Match and If-Modified-Since
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Modified-Since: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'),
+      format_string('If-None-Match: "!checksum"', array(
+        '!checksum' => $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(304);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Modified-Since: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'),
+      format_string('If-None-Match: "!checksum"', array(
+        '!checksum' => 'dont-match' . $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(200);
+    $result = $this->drupalGet("islandora/object/{$object->id}/datastream/{$datastream->id}/view", array(), array(
+      'If-Modified-Since: ' . $datastream->createdDate->sub(new DateInterval('P1M'))->format('D, d M Y H:i:s \G\M\T'),
+      format_string('If-None-Match: "!checksum"', array(
+        '!checksum' => $datastream->checksum,
+      )),
+    ));
+    $this->assertResponse(200);
+  }
+}