What explains the adoption of the regime of cooperation between church and the state in the democratic constitutions of Spain and Poland, while Portugal maintained a regime of strict separation in the United States and French tradition? The explanation could be that a consensual constitution-making process resulted in a constitutional formula accommodating religion and guaranteeing religious freedoms. Alternatively, the constitutional regime of cooperation could result from the diffusion of international norms to national constitutions, in this case, the cosmopolitan law of the church. The article process-traces the constitution drafting processes and finds that the emergence of a constitutional consensus among secularist and constitutional drafters in Spain and Poland was based on the Vatican Council II doctrine and facilitated by the intervention of the Catholic hierarchies. In Portugal, the violent context of the revolution excluded the church, and the constitutional regime of strict separation between church and state was adopted.