This chapter argues that Europe and Islam are in conflict, because European secularism and traditional Islam are based on different world views and both need to adapt in their mutual encounter: Europe by reacquainting itself with its specifically Christian roots within the context of secularism, Islam by adapting itself to a new European context marked by different values. European enlargement and transnational Islam are heading toward a fateful choice, not an unavoidable clash. The Europeanization of Islam, properly understood, will benefit both, Europe and Islam. The Islamization of Europe will be of enormous cost to both Europe and progressive elements in Islam. Some parts of my argument contradict fashionable and comfortable notions that Europe's encounter with Islam, in the form of immigration and European enlargement, will bring into reach the multiculturalism that has eluded Europe for so long. This is the argument of Hakan Yavuz in chapter 9 of this book. Nothing could be further from the truth. The eventual outcome of the renewed encounter between Europe and Islam is far from clear. It depends on how European states and the European Union will react to the growing number of Muslims in their midst and which strand of Islam will eventually prevail politically in Europe's Islamic diaspora, in Turkey, and in the Islamic world at large. Rather than hoping for the best outcome and hiding unpleasant realities, this chapter provides the descriptive analysis that identifies the players, most of them not known to specialists in European affairs or international relations, and the enormous political stakes.