11

After a decade of political, electoral and government changes, the Catalan political parties evolved into a much more polarized situation in the center-periphery axis in late 2012. Starting from the definition of party system given by Peter Mair, the article argues that this development is in part the result of changes in party competition that occurred in Catalonia since 1999. The loss of government by CiU, the rise of ERC and the formation of the leftist tripartite executive altered the patterns of competition existing in previous years. The evolution towards a more open party system led to changes in leadership, in party platforms and in the intraparty factional balance within major parties, which also fostered the creation of new parties. Our conclusions contribute to explaining party radicalization in Catalonia, as well as confirming the utility of a party system approach more focused on the struggle for government.