Abstract EU institutional reforms are far from trivial, as the recent rejection of the treaty establishing a Constitution for Europe by the French and Dutch electorate has demonstrated. With the exception of this treaty, all other treaties in the process of European institution building have been approved by the member states’ governments. In this paper, we ask how these governments reach a decision on EU institutional reforms. Do they engage in coalition formation as is often observed in intergovernmental negotiations? It is our hypothesis that they do not necessarily engage in coalition formation but in peer coordination in policy networks to reach decisions in these multilateral, multiple issue, multi-stage negotiations. In order to test our theory we have implemented a simulation model which we apply to the EU Intergovernmental Conference of 1996 which led to the Amsterdam treaty. We conclude by discussing policy implications of our approach.