When the Eurostat-OECD PPP Programme was established in the early 1980s, only OECD Member Countries were covered, benchmark comparisons were made every five years and all data were collected over an 18 month period centred on the reference year. Organisation was straightforward. Eurostat was responsible for those OECD Member Countries that were also Members of the European Union and the OECD was responsible for those OECD Member Countries that were not. This division of responsibilities has changed with time mainly as the result of the enlargement of the European Union1 (and, but to a lesser extent, of the OECD) and the sizeable jump in the number of countries participating in the Programme that occurred during the second half of the 1990s2. The evolution of Eurostat and OECD responsibilities is charted in Annex I which provides a brief history of the Programme.