A web page may be rendered for display on a client device. The rendered web page may include a first document and a first advertisement that is based on the first document. It may be determined that a first scroll position of the rendered web page has a first characteristic. Possibly responsive to determining that the first scroll position of the rendered web page has the first characteristic, a second document may be requested and received from a content server device, and, based on the second document, a second advertisement may be requested and received from an advertisement server device. The web page may be re-rendered for display on the client device. The re-rendered web page may include content from the first document, content from the second document, the first advertisement, and the second advertisement.