this specification describes technologies relating to content presentation . in general , one aspect of the subject matter described in this specification can be embodied in methods that include the actions of receiving a request to serve a content item to an application on a mobile device ; identifying a context associated with the application , the context being derived from an application description page for the application and one or more pages linking to the application description page , the context comprising one or more keywords associated with the application ; selecting a content item , from a collection of content items , using the context ; and serving the selected content item to the application on the mobile device . other embodiments of this aspect include corresponding systems , apparatus , and computer program products .