Scrolling Interstitial Advertisements

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for providing advertisements for initial off-screen insertion over publisher resources. In one aspect, a method includes receiving, from a user device, a request for a content item for presentation with a publisher resource; and providing, to the user device, a content item with instructions that cause the content item to be inserted into the publisher resource at a location at which at least a portion of the content item is not presented by the user device upon initial presentation of the publisher resource, the instructions further causing the content item to be inserted as an overlay relative to content of the publisher resource and to scroll at a different rate than the content of the publisher resource in response to user interaction with a resource scroll control.