The aim of the study is to examine the extent to which Muslim congregations in Sweden cooperate with organizations in the public and voluntary sectors and to identify the internal and external organizational factors that favour or disfavour such cooperation. The study is based on a nationwide survey of local Muslim congregations (n = 105), and is the first survey of its kind in Europe. Like many other voluntary organizations, Muslim congregations work in cooperation with other voluntary organizations, but also with various institutions run by the local authorities. In Sweden, cooperation between different organizations is strongly encouraged, which results in a system that provides the congregations with opportunity structures. Other factors that influence the degree of cooperation include whether the congregation feels support or opposition from the surrounding community and the local demographic and socio-economic situation: there is a higher degree of cooperation in small municipalities with many social problems. Ethnic heterogeneity is one of the major organizational factors that affect the degree of cooperation. congregations that have an open attitude towards different Muslim traditions, which essential for a multiethnic congregation, are also those most interested in cooperation with other organizations and institutions. Irrespective of whether they belong to a national umbrella organization or not, Muslim congregations in Sweden are in priciple independent local organizations. It is therefore difficult for Islam in Sweden to operate on a national level, in the way that other more established voluntary organizations do. On the other hand, this study shows that while they lack a united voice on the national arena, they have the advantage of flexibility arising from their local autonomy.