The Muslim population of Western Europe composed of atleast 13 million individuals, brings together primarily peopleresulting from working class immigrants from the secondhalf of the twentieth century. Its roots are found deep in theTurkish countryside, in the Balkans and, of course, in the oldcolonies: the countries of the Maghreb, the Indo-Pakistanisub-continent, the Middle East, sub-Saharan Africa andSoutheast Asia. There exists moreover, relatively low butgrowing numbers, of converts of European extraction. Thispaper presents the theoritical and methodological approachof whole of the project "Faiths and Social cohesion".