1. A computer implemented method for delivering content to a client computer over a computer network, the method comprising: managing audience segments using segment-targeting cookies stored on the client computer which each include a segment identifier that indicates an audience segment of which the client computer is a member, and wherein said audience segments correspond to a computer network of audience member information collection domains including a first domain and a second domain that is separate from the first domain; receiving an indication that a client computer has a first attribute based upon information collected in association with activity by the client computer in the first domain; receiving an indication that the client computer has a second attribute based upon information collected in association with activity by the client computer in the second domain; storing the indications of the first and second attributes in a database as profile data; determining from the stored profile data that the client computer is a member of a network segment that is defined to include client computers having the first attribute and the second attribute; transmitting the content over the computer network to the client computer based on the client computer being a member of the network segment; and displaying the content on a display associated with the client computer.