This paper evaluates rational choice models of political participation both at the theoretical and empirical levels. The theoretical discussion is concerned with evaluating attempts which have been made to circumvent the paradox of participation-the proposition introduced by Mancur Olson that rational actors will not get involved in collective action in order to achieve common goals. The analysis suggests that the paradox is more of an intractable problem for rational choice theory than is commonly recognized. The empirical section of the paper uses data from the first national survey of Conservative party members in Britain to model the determinants of political activism. It tests rational actor models against an alternative "general incentives" theory of participation which includes variables that are not consistent with rational choice theory. The conclusion is that while a rational choice model gives great insights into political participation, it provides an incomplete account of participation, and by implication this may be true of such models in other areas of political science.