Almost all new parties that have broken into and established themselves in the “frozen” party systems of Western Europe, including Regionalists, Greens, and Right-wing populists, have roots in social movements. Why have only movement parties been able to become and stay electorally competitive? Contrary to common assumptions in the literature (Michels 1915; Ostrogorski 1902; Kitschelt 2006) and unlike older movement parties like the Social Democrats, these parties are not transitory phenomena on their way to becoming mainstream parties. Instead they continue to provide programmatic and participatory linkages by maintaining clear policy commitments and possibilities to participate in intra-party decision making. I argue that movement parties have found a stable electoral base because their supply of these linkages is matched by a demand from a subgroup of the electorate that is highly politically engaged, but disillusioned with the established catch-all parties and their diluted policy positions.
