This paper develops and tests a theory to explain the routine lobbying of political parties by interest groups on policy issues that they are most active upon. The standard explanation for group/party interactions offered by the ‘friends and foe’ literature is based on ideological congruence, with more recent work highlighting the role of relative party power. This paper advances this understanding by explaining how the impact of ideology on the presence of a lobby routine is conditional on power and policy area. Our results help us understand how power and ideology shape the interaction between interest groups and parties, and ultimately shape policy making, in particular issue areas. We examine interest group lobby routines in different policy domains using a unique survey of representative samples of interest groups across seven democracies, finding support for our predictions.