<p>A system is disclosed that uses behavioral data collected by ISPs (104) and/or other types of data, such as demographic and/or survey data, to categorize particular ISP subscribers (106). The ISP subscribers are assigned to particular categories or "segments" using a segmentation schema (110) that maps particular subscriber behaviors to particular segments. The subscriber-to-segment mappings (116) are made available to content targeting entities (108) via a query interface (120) that, for example, supports queries of the form "what are the segments associated with IP address X?"</p>
