Between September 2009 and April 2011, around one-half of the Catalan municipalities held unofficial referendums on independence from Spain, in which more than 800,000 citizens took part. However, the participation rates were unevenly distributed across Catalonia. In this paper, using an original data set, we aim to respond to two relevant questions: first, why in some municipalities the referendum took place and in others it did not occur. Second, why did the referendum achieve high rates of turnout in some localities and much lower participation in others. We find that the resources available to the movement, the intensity of the mobilization efforts, the participatory tradition of the municipalities and the size of the nationalist 'sentiment pool' in each locality explain to a great extent the internal variation in nationalist mobilization in Catalonia. © The author(s) 2012. Nations and Nationalism © ASEN/Blackwell Publishing Ltd 2012.