Features are disclosed for enabling users to select portions of content pages, including predefined portions and arbitrarily defined portions, for which to receive update notifications or which to share with other users. Notifications regarding updates to the selected portions may be displayed to the user in a notification overlay. The notification overlay may be at least partially transparent so as to allow users to see content on a content page displayed beneath the overlay. The notification overlay may be displayed persistently as the user navigates or otherwise transitions from page to page. Users may also access shared, predefined, and context-sensitive notification overlays created by other users, entities, or automated processes.