The secularization of Western European politics and society has created new constraints but also new opportunity structures for religious bodies. This renewed activism of religious actors in the European public spheres needs to be analysed on specific issues. Immigration, ethical debates or education are well-known illustrations, but ethnonational conflicts are also relevant issues. In that respect, the Basque conflict, on the Franco-Spanish borderland, is a good example of the transformations of the Catholic Church‟s activism in a secularized environment. It is argue that the Church is trying to develop a new register of intervention in the Basque conflict by fostering its role as a mediator. The Church and other actors close to it are particularly active in the making rather than in the process of peace, which would require some basic social agreement on the way to follow. However, the Church‟s commitment to mediation has not gone smoothly, notably on account of the controversy over its impartiality, independence and absence of decision-making power. Though its expertise in mediation has been widely acknowledged, the Church has also been forced to come to terms with history, as though the burden of memory periodically acted as a nemesis for the religious, political and social actors. Finally, the Catholic Church‟s contribution to peace-making can only be apprehended through the double perspective of the secularisation of Basque society and the redefinition of the relationships between religion, the public space and democracy.< Réduire