Bipartisan bills are frequent in presidential systems, but they exist in virtually all parliamentary systems. In fact, despite the predominance of governments in legislative agenda-setting in parliamentary systems, considerable shares of both introduced and successful bills are (co-)sponsored by individuals or party groups that belong to both the government and the opposition camp in parliament. Given the government–opposition divide in parliamentary systems this requires explanation. In this paper, we seek to address the reasons for the introduction and passage of bipartisan bills in parliamentary democracies – bills that originate with government and opposition party actors. To answer this question in a comparative framework, we develop a simple model that links institutional and policy-related characteristics to the likelihood of a bipartisan sponsorship of bills. More specifically, we look at the effect of divided and minority government, heterogeneity of government coalitions, polarization of parliament and issue salience. Our statistical analysis uses original data for about 11,000 bills in two parliamentary systems, Belgium and Germany, 1986–2003.
