diff --git a/.eslintrc.json b/.eslintrc.json
index 7b83892ba3..9efcbc9af5 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -171,6 +171,7 @@
         "unread_ops": false,
         "upload": false,
         "user_events": false,
+        "widgetize": false,
         "submessage": false,
         "Plotly": false,
         "emoji_codes": false,
diff --git a/static/js/submessage.js b/static/js/submessage.js
index 7adf3cc4fc..45e72f0118 100644
--- a/static/js/submessage.js
+++ b/static/js/submessage.js
@@ -15,7 +15,6 @@ exports.get_message_events = function (message) {
         return;
     }
 
-    // The server should sort messages for us, but this is defensive.
     message.submessages.sort(function (m1, m2) {
         return parseInt(m1.id, 10) - parseInt(m2.id, 10);
     });
@@ -45,11 +44,52 @@ exports.process_submessages = function (in_opts) {
     }
 
     blueslip.info('submessages found for message id: ' + message_id);
+
+    var row = in_opts.row;
+
+    // Right now, our only use of submessages is widgets.
+
+    var data = events[0].data;
+
+    if (data === undefined) {
+        return;
+    }
+
+    var widget_type = data.widget_type;
+
+    if (widget_type === undefined) {
+        return;
+    }
+
+    var post_to_server = exports.make_server_callback(message_id);
+
+    widgetize.activate({
+        widget_type: widget_type,
+        extra_data: data.extra_data,
+        events: events,
+        row: row,
+        message: message,
+        post_to_server: post_to_server,
+    });
 };
 
 
 exports.handle_event = function (event) {
     blueslip.info('handle submessage: ' + JSON.stringify(event));
+
+    // Right now, our only use of submessages is widgets.
+    var msg_type = event.msg_type;
+
+    if (msg_type !== 'widget') {
+        blueslip.warn('unknown msg_type: ' + msg_type);
+        return;
+    }
+
+    widgetize.handle_event({
+        sender_id: event.sender_id,
+        message_id: event.message_id,
+        data: event.data,
+    });
 };
 
 exports.make_server_callback = function (message_id) {
diff --git a/static/js/widgetize.js b/static/js/widgetize.js
new file mode 100644
index 0000000000..2e78417984
--- /dev/null
+++ b/static/js/widgetize.js
@@ -0,0 +1,77 @@
+var widgetize = (function () {
+
+var exports = {};
+
+var widgets = {};
+
+exports.activate = function (in_opts) {
+    var widget_type = in_opts.widget_type;
+    var extra_data = in_opts.extra_data;
+    var events = in_opts.events;
+    var row = in_opts.row;
+    var message = in_opts.message;
+    var post_to_server = in_opts.post_to_server;
+
+    events.shift();
+
+    if (!widgets[widget_type]) {
+        blueslip.warn('unknown widget_type', widget_type);
+        return;
+    }
+
+    var content_holder = row.find('.message_content');
+
+    var widget_elem;
+    if (message.widget) {
+        // Use local to work around linter.  We can trust this
+        // value because it comes from a template.
+        widget_elem = message.widget_elem;
+        content_holder.html(widget_elem);
+        return;
+    }
+
+    var callback = function (data) {
+        post_to_server({
+            msg_type: 'widget',
+            data: data,
+        });
+    };
+
+    // We depend on our widgets to use templates to build
+    // the HTML that will eventually go in this div.
+    widget_elem = $('<div>');
+    content_holder.html(widget_elem);
+
+    var widget = widgets[widget_type].activate({
+        elem: widget_elem,
+        callback: callback,
+        message: message,
+        extra_data: extra_data,
+    });
+
+    // This is hacky, we should just maintain our own list.
+    message.widget = widget;
+    message.widget_elem = widget_elem;
+
+    // Replay any events that already happened.  (This is common
+    // when you narrow to a message after other users have already
+    // interacted with it.)
+    if (events.length > 0) {
+        widget.handle_events(events);
+    }
+};
+
+exports.handle_event = function (widget_event) {
+    var message = message_store.get(widget_event.message_id);
+
+    var events = [widget_event];
+
+    message.widget.handle_events(events);
+};
+
+return exports;
+
+}());
+if (typeof module !== 'undefined') {
+    module.exports = widgetize;
+}
diff --git a/tools/compile-handlebars-templates b/tools/compile-handlebars-templates
index 27ba19d7d0..5006d32443 100755
--- a/tools/compile-handlebars-templates
+++ b/tools/compile-handlebars-templates
@@ -22,7 +22,8 @@ STATIC_PATH = 'static/'
 def get_templates():
     # type: () -> List[str]
     return (glob.glob(os.path.join(STATIC_PATH, 'templates/*.handlebars')) +
-            glob.glob(os.path.join(STATIC_PATH, 'templates/settings/*.handlebars')))
+            glob.glob(os.path.join(STATIC_PATH, 'templates/settings/*.handlebars')) +
+            glob.glob(os.path.join(STATIC_PATH, 'templates/widgets/*.handlebars')))
 
 def run():
     # type: () -> None
diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index b786ada982..07b8ecab67 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -189,7 +189,7 @@ def build_custom_checkers(by_lang):
         {'pattern': '\+.*i18n\.t\(.+\)',
          'description': 'Do not concatenate i18n strings'},
         {'pattern': '[.]html[(]',
-         'exclude_pattern': '[.]html[(]("|\'|templates|html|message.content|sub.rendered_description|i18n.t|rendered_|$|[)]|error_text|[$]error|[$][(]"<p>"[)])',
+         'exclude_pattern': '[.]html[(]("|\'|templates|html|message.content|sub.rendered_description|i18n.t|rendered_|$|[)]|error_text|widget_elem|[$]error|[$][(]"<p>"[)])',
          'exclude': ['static/js/portico', 'static/js/lightbox.js', 'static/js/ui_report.js',
                      'frontend_tests/'],
          'description': 'Setting HTML content with jQuery .html() can lead to XSS security bugs.  Consider .text() or using rendered_foo as a variable name if content comes from handlebars and thus is already sanitized.'},
diff --git a/zproject/settings.py b/zproject/settings.py
index a1d5916600..4bda41da92 100644
--- a/zproject/settings.py
+++ b/zproject/settings.py
@@ -947,6 +947,7 @@ JS_SPECS = {
             'js/top_left_corner.js',
             'js/stream_list.js',
             'js/filter.js',
+            'js/widgetize.js',
             'js/submessage.js',
             'js/fetch_status.js',
             'js/message_list_data.js',