diff --git a/tildes/scss/_base.scss b/tildes/scss/_base.scss
index 4dc080b..abf5f26 100644
--- a/tildes/scss/_base.scss
+++ b/tildes/scss/_base.scss
@@ -142,6 +142,7 @@ main {
 
 menu {
   list-style-type: none;
+  padding: 0;
 }
 
 // We'll use lists for their semantic value sometimes, so we don't want them to
diff --git a/tildes/scss/modules/_tab.scss b/tildes/scss/modules/_tab.scss
index 9bb1faa..3e4c59c 100644
--- a/tildes/scss/modules/_tab.scss
+++ b/tildes/scss/modules/_tab.scss
@@ -1,6 +1,20 @@
 // Copyright (c) 2018 Tildes contributors <code@tildes.net>
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
+.tab {
+  font-size: 0.6rem;
+}
+
+.tab-item {
+  &.active .btn {
+    border-bottom: 2px solid;
+  }
+
+  .btn {
+    font-weight: normal;
+  }
+}
+
 .tab-listing-order {
   flex-wrap: nowrap;
   padding-left: 0;
@@ -8,8 +22,6 @@
 
   justify-content: space-around;
 
-  font-size: 0.6rem;
-
   // have the tabs span the full width at small sizes
   width: 100%;
   @media (min-width: $size-md) {
@@ -31,3 +43,7 @@
     }
   }
 }
+
+.tab-markdown-mode {
+  display: inline-flex;
+}
diff --git a/tildes/scss/themes/_theme_base.scss b/tildes/scss/themes/_theme_base.scss
index 20b6dac..e1738c8 100644
--- a/tildes/scss/themes/_theme_base.scss
+++ b/tildes/scss/themes/_theme_base.scss
@@ -405,7 +405,7 @@
     background-color: map-get($theme, "alert");
   }
 
-  .tab-listing-order {
+  .tab {
     border-color: map-get($theme, "border");
   }
 
@@ -414,7 +414,8 @@
       color: map-get($theme, "foreground-primary");
     }
 
-    &.active a {
+    &.active a,
+    &.active button {
       color: map-get($theme, "link");
       border-bottom-color: map-get($theme, "link");
     }
diff --git a/tildes/static/js/behaviors/comment-reply-button.js b/tildes/static/js/behaviors/comment-reply-button.js
index 0fed2ca..38161e3 100644
--- a/tildes/static/js/behaviors/comment-reply-button.js
+++ b/tildes/static/js/behaviors/comment-reply-button.js
@@ -24,6 +24,7 @@ $.onmount('[data-js-comment-reply-button]', function() {
         var parentCommentAuthor = $parentComment.find('header:first .link-user').text();
         var postURL = '/api/web/comments/' + parentCommentID + '/replies';
         var markdownID = 'markdown-reply-' + parentCommentID;
+        var previewID = markdownID + '-preview';
 
         if ($('#' + markdownID).length > 0) {
             $('#' + markdownID).focus();
@@ -39,6 +40,12 @@ $.onmount('[data-js-comment-reply-button]', function() {
         clone.querySelector('span').innerHTML = 'Replying to ' + parentCommentAuthor;
         clone.querySelector('textarea').setAttribute('id', markdownID);
 
+        var preview = clone.querySelector('[data-js-markdown-preview]');
+        preview.setAttribute('id', previewID);
+
+        clone.querySelector('[data-js-markdown-preview-tab] .btn')
+            .setAttribute('data-ic-target', '#' + previewID);
+
         var cancelButton = clone.querySelector('[data-js-cancel-button]');
         $(cancelButton).on('click', function (event) {
             // re-enable click/hover events on the reply button
diff --git a/tildes/static/js/behaviors/markdown-edit-tab.js b/tildes/static/js/behaviors/markdown-edit-tab.js
new file mode 100644
index 0000000..de5f84b
--- /dev/null
+++ b/tildes/static/js/behaviors/markdown-edit-tab.js
@@ -0,0 +1,12 @@
+// Copyright (c) 2018 Tildes contributors <code@tildes.net>
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+$.onmount('[data-js-markdown-edit-tab]', function() {
+    $(this).click(function(event) {
+        var $editTextarea = $(this).closest('form').find('[name="markdown"]');
+        var $previewDiv = $(this).closest('form').find('[data-js-markdown-preview]');
+
+        $editTextarea.removeClass('d-none');
+        $previewDiv.addClass('d-none');
+    });
+});
diff --git a/tildes/static/js/behaviors/markdown-preview-tab.js b/tildes/static/js/behaviors/markdown-preview-tab.js
new file mode 100644
index 0000000..07660e6
--- /dev/null
+++ b/tildes/static/js/behaviors/markdown-preview-tab.js
@@ -0,0 +1,19 @@
+// Copyright (c) 2018 Tildes contributors <code@tildes.net>
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+$.onmount('[data-js-markdown-preview-tab]', function() {
+    $(this).click(function(event) {
+        var $editTextarea = $(this).closest('form').find('[name="markdown"]');
+        var $previewDiv = $(this).closest('form').find('[data-js-markdown-preview]');
+
+        $editTextarea.addClass('d-none');
+        $previewDiv.removeClass('d-none');
+    });
+
+    $(this).on('after.success.ic success.ic', function(event) {
+        // Stop intercooler event from bubbling up past this button. This
+        // prevents behaviors on parent elements from mistaking a successful
+        // "preview" from a successful "submit".
+        event.stopPropagation();
+    });
+});
diff --git a/tildes/static/js/behaviors/tab.js b/tildes/static/js/behaviors/tab.js
new file mode 100644
index 0000000..c18105a
--- /dev/null
+++ b/tildes/static/js/behaviors/tab.js
@@ -0,0 +1,9 @@
+// Copyright (c) 2018 Tildes contributors <code@tildes.net>
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+$.onmount('[data-js-tab]', function() {
+    $(this).click(function(event) {
+        $(this).siblings().removeClass('active');
+        $(this).addClass('active');
+    });
+});
diff --git a/tildes/tildes/routes.py b/tildes/tildes/routes.py
index a805433..59948ce 100644
--- a/tildes/tildes/routes.py
+++ b/tildes/tildes/routes.py
@@ -154,6 +154,8 @@ def add_intercooler_routes(config: Configurator) -> None:
         )
         add_ic_route("user_ban", "/ban", factory=user_by_username)
 
+    add_ic_route("markdown_preview", "/markdown_preview", factory=LoggedInFactory)
+
 
 class LoggedInFactory:
     """Simple class to use as `factory` to restrict routes to logged-in users.
diff --git a/tildes/tildes/templates/intercooler/markdown_preview.jinja2 b/tildes/tildes/templates/intercooler/markdown_preview.jinja2
new file mode 100644
index 0000000..cf82e5d
--- /dev/null
+++ b/tildes/tildes/templates/intercooler/markdown_preview.jinja2
@@ -0,0 +1,4 @@
+{# Copyright (c) 2018 Tildes contributors <code@tildes.net> #}
+{# SPDX-License-Identifier: AGPL-3.0-or-later #}
+
+{{ rendered_html|safe }}
diff --git a/tildes/tildes/templates/macros/forms.jinja2 b/tildes/tildes/templates/macros/forms.jinja2
index 2448bb6..eb3308c 100644
--- a/tildes/tildes/templates/macros/forms.jinja2
+++ b/tildes/tildes/templates/macros/forms.jinja2
@@ -6,14 +6,31 @@
     <span>{{ caption }}</span>
     <a href="https://docs.tildes.net/text-formatting" target="_blank" tabindex="-1">Formatting help</a>
   </label>
-  <textarea
-    class="form-input"
-    id="{{ id }}"
-    name="markdown"
-    placeholder="Text (Markdown)"
-    data-js-ctrl-enter-submit-form
-    {% if auto_focus %}data-js-auto-focus{% endif %}
-  >{% if text %}{{ text }}{% endif %}</textarea>
+  <div class="form-markdown">
+    <menu class="tab tab-markdown-mode">
+      <li class="tab-item active" data-js-tab data-js-markdown-edit-tab>
+        <button type="button" class="btn btn-link">Edit</button>
+      </li>
+      <li class="tab-item" data-js-tab data-js-markdown-preview-tab>
+        <button
+          type="button"
+          class="btn btn-link"
+          data-ic-post-to="/api/web/markdown_preview"
+          data-ic-target="#{{ id }}-preview"
+          data-ic-replace-target="false"
+        >Preview</button>
+      </li>
+    </menu>
+    <textarea
+      class="form-input"
+      id="{{ id }}"
+      name="markdown"
+      placeholder="Text (Markdown)"
+      data-js-ctrl-enter-submit-form
+      {% if auto_focus %}data-js-auto-focus{% endif %}
+    >{% if text %}{{ text }}{% endif %}</textarea>
+    <div id="{{ id }}-preview" class="d-none" data-js-markdown-preview></div>
+  </div>
 {% endmacro %}
 
 {% macro topic_tagging(value=None, auto_focus=False, autocomplete_options=None) %}
diff --git a/tildes/tildes/views/api/web/markdown_preview.py b/tildes/tildes/views/api/web/markdown_preview.py
new file mode 100644
index 0000000..c03c2f1
--- /dev/null
+++ b/tildes/tildes/views/api/web/markdown_preview.py
@@ -0,0 +1,25 @@
+# Copyright (c) 2018 Tildes contributors <code@tildes.net>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+"""Web API endpoint for previewing Markdown."""
+
+from pyramid.request import Request
+from webargs.pyramidparser import use_kwargs
+
+from tildes.lib.markdown import convert_markdown_to_safe_html
+from tildes.schemas.comment import CommentSchema
+from tildes.views.decorators import ic_view_config
+
+
+@ic_view_config(
+    route_name="markdown_preview",
+    request_method="POST",
+    renderer="markdown_preview.jinja2",
+)
+@use_kwargs(CommentSchema(only=("markdown",)))
+def markdown_preview(request: Request, markdown: str) -> dict:
+    """Render the provided text as Markdown."""
+    # pylint: disable=unused-argument
+
+    rendered_html = convert_markdown_to_safe_html(markdown)
+    return {"rendered_html": rendered_html}