The codecision procedure was designed to change the distribution of power among the European Union (EU) institutions. In theory, the codecision procedure, at least the amended version introduced by the Amsterdam Treaty that came into effect in 1999, weakened the Commission and placed the Parliament on an equal footing with the Council. We assess how the codecision procedure works in practice using data on the preferences of legislative actors on a large number of proposals negotiated between 1999 and 2009. We also test theoretical propositions derived from Schelling regarding the effects of policy agreement within each chamber on the relative bargaining success of the Council and EP. Our findings suggest that, in comparison to the consultation procedure, codecision has strengthened the EP and weakened the Commission. However, the Council holds certain bargaining advantages over the EP, and as a result the EP has not achieved parity with the Council under codecision.