CONTEXTUAL CONTENT DISTRIBUTION

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for distributing content based on context are disclosed. In one aspect, a method includes identifying, in a single resource, multiple different content item slots that are available for presentation of multiple different content items. A determination is made that a first content item slot is located in a first portion of the single resource, and that a second content item slot is located in a second different portion of the resource. A first content item is selected for presentation in the first content item slot based on terms that correspond to a first topic of the first portion of the resource. A second content item is selected for presentation in the second content item slot based on terms that correspond to a second topic of the second portion of the resource.