Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for generating additional content. In one aspect, a method includes identifying one or more central entities, wherein each central entity represents a topic of a first resource being presented in a user interface; generating one or more search queries, each of the one or more search queries being derived from one or more of the central entities; obtaining search results for the one or more search queries from a search engine; selecting resources relevant to the first resource from resources referenced by the obtained search results; generating additional content for presentation in a user interface element of the user interface based on the selected resources; and categorizing the generated additional content into a plurality of categories, wherein each category of additional content is displayed in a separate portion of the user interface element.