Various strands of literature in comparative politics regard governments as the only noteworthy initiator and mainspring of legislative policy-making in parliamentary democracies. Opposition activity in policy-making is thus more often associated with the intention to prevent, rather than shape policy. Does this perception reflect real life politics? To answer this question, we discuss different arguments that link institutional and policy-related characteristics to the incentives and constraints of different government and parliamentary actors to initiate or co-sponsor legislative bills. More specifically, we relate policy-, office- and vote-related incentives as well as institutional and resource constraints of legislative actors to the likelihood that these actors will take the lead in legislative agenda-setting. We confront these arguments with original data on the universe of all legislative bills in four parliamentary systems over one and a half decades. We find that opposition and in particular bipartisan agenda-setting is indeed rare. Yet, in contrast to widely held maxims, it is neither absent nor spurious but related to the allocation of power and the intensity of ideological conflict both within and between the (coalition) government and parliament.