How do foreign policy beliefs affect German parliamentarians’ (MPs) support for European integration? Despite important advances, the literature has overlooked the effect of foreign policy beliefs on national representatives’ attitudes toward integration. This study provides a systematic investigation of the role foreign policy beliefs play in shaping German MPs’ support for European integration. I argue that given the complex and contentious character of European integration politics MPs derive heuristic cues from their foreign policy beliefs to form opinions on the desirability of integration. Using data from an original survey conducted with members of the seventeenth German Bundestag, I show that a belief in multilateralism increases support for European integration while isolationist and hawkish foreign policy orientations decrease support. These results indicate that support for European integration is not merely determined by party ideology, electoral pressure or economic considerations, but also has a psychological foundation shaped by politicians’ core beliefs about how the world of international politics operates.