Abstract
The role of political parties in developing public policy is a thoroughly understudied topic. We argue that, to understand the role of formal party organizations in the policy process, researchers must examine the relationship between parties and ideologically similar but informally affiliated groups – called the ‘extended party network’ (EPN) – such as interest groups and think tanks. We show that parties are focused on electoral pursuits and should thus be viewed as demanders of policy ideas. The organizations in their extended network, however, have the resources and incentives to invest in developing public policy ideas. We argue that groups in the EPN supply their preferred party with policy ideas, and formal party actors filter these ideas and choose a policy proposal acceptable to these supporters. Conceiving of parties beyond their formal organizations should therefore clarify their role in the policy process.