diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 81b0c99..f65089f 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -973,7 +973,9 @@ function book_preprocess_block(&$variables) {
 }
 
 /**
- * Processes variables for book-all-books-block.tpl.php.
+ * Prepares variables for book listing block templates.
+ *
+ * Default template: book-all-books-block.twig.html.
  *
  * All non-renderable elements are removed so that the template has full access
  * to the structured data but can also simply iterate over all elements and
@@ -982,8 +984,6 @@ function book_preprocess_block(&$variables) {
  * @param array $variables
  *   An associative array containing the following key:
  *   - book_menus
- *
- * @see book-all-books-block.tpl.php
  */
 function template_preprocess_book_all_books_block(&$variables) {
   // Remove all non-renderable elements.
@@ -995,13 +995,13 @@ function template_preprocess_book_all_books_block(&$variables) {
 }
 
 /**
- * Processes variables for book-navigation.tpl.php.
+ * Prepares variables for book navigation templates.
+ *
+ * Default template: book-navigation.twig.html.
  *
  * @param array $variables
  *   An associative array containing the following key:
  *   - book_link
- *
- * @see book-navigation.tpl.php
  */
 function template_preprocess_book_navigation(&$variables) {
   drupal_add_css(drupal_get_path('module', 'book') . '/book.theme.css');
@@ -1117,15 +1117,15 @@ function book_toc($bid, $depth_limit, $exclude = array()) {
 }
 
 /**
- * Preprocesses variables for book-export-html.tpl.php.
+ * Prepares variables for book export templates.
+ *
+ * Default template: book-export-html.twig.html
  *
  * @param array $variables
  *   An associative array containing the following keys:
  *   - title
  *   - contents
  *   - depth
- *
- * @see book-export-html.tpl.php
  */
 function template_preprocess_book_export_html(&$variables) {
   global $base_url;
@@ -1207,14 +1207,14 @@ function book_node_export(Node $node, $children = '') {
 }
 
 /**
- * Processes variables for book-node-export-html.tpl.php.
+ * Processes variables for single node export templates.
+ *
+ * Default template: book-node-export-html.html.twig.
  *
  * @param array $variables
  *   An associative array containing the following keys:
  *   - node
  *   - children
- *
- * @see book-node-export-html.tpl.php
  */
 function template_preprocess_book_node_export_html(&$variables) {
   $variables['depth'] = $variables['node']->book['depth'];
diff --git a/core/modules/book/templates/book-all-books-block.html.twig b/core/modules/book/templates/book-all-books-block.html.twig
index 14e665d..241594d 100644
--- a/core/modules/book/templates/book-all-books-block.html.twig
+++ b/core/modules/book/templates/book-all-books-block.html.twig
@@ -9,10 +9,10 @@
  * Available variables:
  * - book_menus: Book outlines.
  *   - book_id: the parent book ID.
- *   - menu: @TODO
+ *   - menu: an array of top-level book links.
  *
- * @see template_preprocess
- * @see template_preprocess_book_all_books_block
+ * @see template_preprocess()
+ * @see template_preprocess_book_all_books_block()
  *
  * @ingroup themeable
  */
diff --git a/core/modules/book/templates/book-export-html.html.twig b/core/modules/book/templates/book-export-html.html.twig
index ecb50f1..1177f4c 100644
--- a/core/modules/book/templates/book-export-html.html.twig
+++ b/core/modules/book/templates/book-export-html.html.twig
@@ -12,8 +12,8 @@
  * - contents: Nodes within the current outline rendered through
  *   book-node-export-html.html.twig.
  *
- * @see template_preprocess
- * @see template_preprocess_book_export_html
+ * @see template_preprocess()
+ * @see template_preprocess_book_export_html()
  *
  * @ingroup themeable
  */
diff --git a/core/modules/book/templates/book-navigation.html.twig b/core/modules/book/templates/book-navigation.html.twig
index a036f9b..8c873f0 100644
--- a/core/modules/book/templates/book-navigation.html.twig
+++ b/core/modules/book/templates/book-navigation.html.twig
@@ -26,8 +26,8 @@
  * - book_title: The book/node title of the current outline being viewed.
  *   Provided as an option. Not used by default.
  *
- * @see template_preprocess
- * @see template_preprocess_book_navigation
+ * @see template_preprocess()
+ * @see template_preprocess_book_navigation()
  *
  * @ingroup themeable
  */
@@ -40,17 +40,17 @@
       <ul class="book-pager">
       {% if prev_url %}
         <li class="previous">
-          <a href="{{ prev_url }}" rel="prev" title="{{ 'Go to previous page' | t }}"><b>{{ '‹' | t }}</b>{{ prev_title }}</a>
+          <a href="{{ prev_url }}" rel="prev" title="{{ 'Go to previous page' | t }}"><b>{{ '‹' | t }}</b> {{ prev_title }}</a>
         </li>
       {% endif %}
       {% if parent_url %}
         <li class="up">
-          <a href="{{ parent_url }}" title="{{ 'Go to parent page' | t }}">{{ 'up' | t }}</a>
+          <a href="{{ parent_url }}" title="{{ 'Go to parent page' | t }}">{{ 'Up' | t }}</a>
         </li>
       {% endif %}
       {% if next_url %}
         <li class="next">
-          <a href="{{ next_url }}" rel="next" title="{{ 'Go to next page' | t }}">{{ next_title }}<b>{{ '›' | t }}</b></a>
+          <a href="{{ next_url }}" rel="next" title="{{ 'Go to next page' | t }}">{{ next_title }} <b>{{ '›' | t }}</b></a>
         </li>
       {% endif %}
     </ul>
diff --git a/core/modules/book/templates/book-navigation.tpl.php b/core/modules/book/templates/book-navigation.tpl.php
deleted file mode 100644
index cdc1278..0000000
--- a/core/modules/book/templates/book-navigation.tpl.php
+++ /dev/null
@@ -1,58 +0,0 @@
-<?php
-/**
- * @file
- * Default theme implementation to navigate books.
- *
- * Presented under nodes that are a part of book outlines.
- *
- * Available variables:
- * - $tree: The immediate children of the current node rendered as an unordered
- *   list.
- * - $current_depth: Depth of the current node within the book outline. Provided
- *   for context.
- * - $prev_url: URL to the previous node.
- * - $prev_title: Title of the previous node.
- * - $parent_url: URL to the parent node.
- * - $parent_title: Title of the parent node. Not printed by default. Provided
- *   as an option.
- * - $next_url: URL to the next node.
- * - $next_title: Title of the next node.
- * - $has_links: Flags TRUE whenever the previous, parent or next data has a
- *   value.
- * - $book_id: The book ID of the current outline being viewed. Same as the node
- *   ID containing the entire outline. Provided for context.
- * - $book_url: The book/node URL of the current outline being viewed. Provided
- *   as an option. Not used by default.
- * - $book_title: The book/node title of the current outline being viewed.
- *   Provided as an option. Not used by default.
- *
- * @see template_preprocess_book_navigation()
- *
- * @ingroup themeable
- */
-?>
-<?php if ($tree || $has_links): ?>
-  <nav id="book-navigation-<?php print $book_id; ?>" class="book-navigation">
-    <?php print $tree; ?>
-    <?php if ($has_links): ?>
-      <h2 class="element-invisible"><?php print t('Book Navigation'); ?></h2>
-      <ul class="book-pager">
-      <?php if ($prev_url): ?>
-        <li class="previous">
-          <a href="<?php print $prev_url; ?>" rel="prev" title="<?php print t('Go to previous page'); ?>"><b><?php print t('‹'); ?></b> <?php print $prev_title; ?></a>
-        </li>
-      <?php endif; ?>
-      <?php if ($parent_url): ?>
-        <li class="up">
-          <a href="<?php print $parent_url; ?>" title="<?php print t('Go to parent page'); ?>"><?php print t('Up'); ?></a>
-        </li>
-      <?php endif; ?>
-      <?php if ($next_url): ?>
-        <li class="next">
-          <a href="<?php print $next_url; ?>" rel="next" title="<?php print t('Go to next page'); ?>"><?php print $next_title;?> <b><?php print t('›'); ?></b></a>
-        </li>
-      <?php endif; ?>
-    </ul>
-    <?php endif; ?>
-  </nav>
-<?php endif; ?>
diff --git a/core/modules/book/templates/book-node-export-html.html.twig b/core/modules/book/templates/book-node-export-html.html.twig
index bb95385..f8da328 100644
--- a/core/modules/book/templates/book-node-export-html.html.twig
+++ b/core/modules/book/templates/book-node-export-html.html.twig
@@ -3,18 +3,15 @@
  * @file
  * Default theme implementation for a single node in a printer-friendly outline.
  *
- * @see book-node-export-html.html.twig
- *   Where it is collected and printed out.
- *
  * Available variables:
- * - node: @TODO
+ * - node: Fully loaded node entity.
  * - depth: Depth of the current node inside the outline.
  * - title: Node title.
  * - content: Node content.
  * - children: All the child nodes recursively rendered through this file.
  *
- * @see template_preprocess
- * @see template_preprocess_book_node_export_html
+ * @see template_preprocess()
+ * @see template_preprocess_book_node_export_html()
  *
  * @ingroup themeable
  */