Since 1996 the global interactive media industry has been striving to demonstrate accountability. Similarly in 1930 print media advertisers began to insist on independent measurement of circulation. They were also working on early versions of research into readership. The same was true later for radio, TV, exhibitions and ambient media. The fundamental difference for interactive media was the opportunity to start the process globally. This was never and is still not the case for any other medium. Different measurement providers around the world (and competing companies in the same country) still use different definitions for a paid copy of a newspaper, for example. This paper discusses the two ways that website traffic can be measured as well as various methodologies that are used to analyse server based traffic data. Case studies are provided.