The map of Europe is deceptively simple as far as TV measurement is concerned. The same technique (a panel equipped with electronic set and people meters) is used in every country, or will be by the end of the year, and only 2 companies, AGB and GFK, control these panels in every country except France, Finland and Sweden. In practice, the meaning of a TV rating is different in every single country (and sometimes within countries), and key measures, such as viewing minutes, channel share and even audience demographics cannot be compared between countries because of the different ways in which they are calculated. This paper describes how this situation has developed, and why it is now likely to change. It details the main data needs of advertising agencies and advertisers from TV audience research, and then specifies those elements which currently have most effect on the differences between these measures in different European countries.