This essay examines the causes of government support for European integration. It evaluates several competing theories, both material and ideological. Two dependent variables are examined: government support for European integration in Council of Ministers decisions, and in the 1997 Amsterdam intergovernmental conference. There appear to be sharp differences between the two decision-making fora in the efficacy of predictive variables. In the Council of Ministers, left–right political ideology and financial transfers from the European Union to member states provide the best explanations. In the Amsterdam conference, experience in the Second World War and financial transfers provide the best explanations. This research extends our understanding of why governments choose co-operation within the European Union. It also extends our understanding of the relationship between ideology and integration preferences. Ideology matters not just to parties, but also to governments, which represent both territorial interests and ideologies. There appears to be a linear relationship, whereby left governments are more supportive of integration than right governments.