The relationship between a party leadership and party activists is often illustrated by the use of John May’s "Law of curvilinear opinion structures in political parties", i.e. the idea that mid-level party activists are assumed to be more radical than both party sympathisers and the party elite. This tension between party leadership and party activists can be assumed to lead to a restriction on the party leadership’s freedom of action. However, in recent years we have seen a number of examples where political parties have made major realignments of their own policies without any substantial internal conflicts. Given the role assigned to conditions for involvement in the formulation of May's Law it appears reasonable to look in that direction when trying to understand these changes. This study covers the Moderate Party, the Social Democratic Party and the Green Party in Sweden. The offer made by the parties to their members can be understood in terms of collective goods, such as ideological and political community, and selective goods, such as elected offices. This thesis shows how the political involvement for the interviewed party activists is intimately linked to selective goods. This finding can help us to understand ideological and political changes in present-day parties. If, as a party activist, one is attracted by the opportunities to become an elected representative or the opportunities to exercise political power, it is reasonable to imagine that one will be more inclined to support actions that increase the opportunity to enjoy these goods. Since both the party leadership and the party activists are attracted by the selective goods offered by the party organisation, the conflict between these groups decreases, as both groups are focused on winning elections and exercising political power. The result of this study therefore provides grounds for questioning the ideas of a tension between party activists and party leaderships.