"This paper measures changes in Western European political party systems and in particular in the political spectrum and in party positioning within that spectrum. Changes are measured using two directly comparable expert surveys of party positions on four core policy dimensions, conducted in 1989 and 2003. The paper distinguishes between three different types of parties: "survivor" parties, which competed in both 1989 and 2003; "new" parties, which competed in 2003 but not 1989; and "extinct" parties, which competed in 1989 but not 2003. The principal findings reveal, firstly, changes in the relative importance of core policy dimensions as well as correlations between party positions on these dimensions. Secondly, the findings show historical trends in the political stances of European parties, and, most strikingly, a clear tendency for new parties to emerge and for old parties to disappear at the two extremes of the political spectrum."