This book offers a systematic and far-reaching account of party system institutionalization in Western Europe. Drawing upon a wide array of data and through a comparison of 20 countries from the end of WWII to 2019 across three arenas of party competition (electoral, parliamentary, and governmental ones), the empirical analysis shows that, over the past decade, the level of institutionalization in the Western European party systems has dramatically declined compared with previous decades. Electoral, parliamentary, and – in some cases – governmental instability and unpredictability have...