Although membership in voluntary associations has been presumed to be a central element in the building of social capital, micro-level knowledge about whether and how voluntary associations make their members more trusting and cooperative has been lacking. The link between trust and involvement in associations in Germany and Sweden was explored by means of a questionnaire concerning traits of individuals and of the associational groups to which they belong. The analysis of the resulting data set considered the extent to which various group characteristics (such as demographic diversity, in-group trust, and engagement level) are related to the generalized trust of the members. The results indicate that more diverse, more engaged voluntary associations, and those with weak ties, indeed accommodate more trusting people. In particular, time spent in groups with foreigners, or in groups with weaker ties, affectsthe generalized trust levels of the members.