This article analyzes and compares the politics of European policy-making within the British Labour Party, the Parti Socialiste (PS) and the Sozialdemokratische Partei Deutschlands (SPD) between 1997 and 2012. We know that party leaders have assumed much autonomy in the making of European policy, but, as with policy-making in any area, their autonomy is constrained and sometimes even questioned by other parts of the party. In order to establish how they are constrained, and what factors increase the level of constraint, this study explores the roles played by four party actors in the making of European policy: conferences, national executive committees, Members of Parliament and Members of the European Parliament. This article, which is based on over 35 interviews with EU experts from the three parties, confirms that European policy was generally made by the party leadership. Other party actors, however, were able to influence the leadership on a small number of occasions. The extent of their influence depended upon the polity, party, policy and politics.