This dissertation investigates the obstacles to membership influence on policy in political parties. It outlines and critiques the two most common theories of Intra-party democracy: one, labelled the 'decline theory', arguing that members have lost influence; the other, labelled the 'oligarchy theory' and based on Michels' work, arguing that intra-party democracy is impossible because of the inherent oligarchic tendencies in all organisations, in their stead the dissertation develops an alternative theory, labelled 'variable membership influence' (VMl). VMl develops Michels' 'iron law of oligarchy' by showing how the forces that drive oligarchy identified by Michels do not affect all parties universally. instead they are presented as being contextual and variable depending on the attitudes and ambitions of party members and leaders, as well as the political environment in which a party operates.