Framing plays an important role in public policy. Interest groups strategically highlight some aspects of a policy proposal while ignoring others in order to gain an advantage in the policy debate. However, we know remarkably little about how interest groups choose their frames. This contribution therefore studies the determinants of frame choice during the policy formation stage in the European Union. We argue that frame choice is a complex process which is simultaneously affected by interest groups as well as contextual characteristics. With regard to interest group characteristics, we expect that frame choice varies systematically across actor type. With regard to contextual characteristics, we hypothesize that the frames that interest groups employ are specifically tailored towards the DGs in charge of drafting the proposal. Our theoretical expectations are tested based on a new and innovative dataset on frame choice of more than 3,000 interest gropus in 44 policy debates.