The decline of party activism and membership in European democracies has been well documented, but not effectively explained. This article examines the state of party membership and activism across a wide spectrum of democratic countries and shows that membership is in decline in most of them. It tests two rival explanations of the decline using a cross-sectional multi-level analysis of data from the ISSP Citizenship survey of 2004. One hypothesis is that the decline is due to ‘state capture’, or excessive state regulation brought about by an ever-closer relationship between parties and the state which has the effect of stifling voluntary activity at the grassroots level. A second suggests that parties are being undermined by the growth of relatively new forms of participation, notably cheque book participation, and consumer and Internet participation. These provide alternative outlets for political action outside traditional forms of participation such as party involvement. There is evidence to support the first of these hypotheses, but not the second.