This dataset identifies and lists all the new parties emerged in Western Europe since 1945 and provides data about party system innovation, defined as the aggregate level of ‘newness’ recorded in a party system at a given election. Data are based on parliamentary elections (lower house) of 19 Western European countries since 1945. This dataset covers the entire universe of Western European elections held after World War II under democratic regimes. Data for Greece, Portugal and Spain have been collected after their democratizations in the 1970s. This dataset follows the recent publication of an article [Emanuele, V. and Chiaramonte, A. (2016), 'A growing impact of new parties: myth or reality? Party system innovation in Western Eur...