Methods, systems, and apparatus, including computer programs encoded on computer storage media, for an audience of network devices. One of the methods includes receiving information from a source, the information associated with a device identifier. The method includes determining, based on the device identifier, a unique user identifier, wherein the unique user identifier identifies a user independent of network, media, and location. The method includes identifying at least one user attribute based on the received information. The method includes associating the user attribute with the unique user identifier. The method also includes storing the user attribute in a repository. The repository stores a plurality of other user attributes associated with the unique user identifier, the other stored user attributes being received from a plurality of different sources.