Social capital theory expects volunteering to generate general social trust, while critics point out that there is little evidence to support this claim. The purpose of this article is to show that volunteering can cause trust, depending on the institutional context and the types of organizations for which people volunteer. The data are from representative population surveys conducted in Norway and the Czech Republic in 2009. The analysis shows that in institutional contexts with impartial and reliable institutions, as in the case of Norway, general social trust is very high in comparative perspective, and the experience of volunteering has little additional effect. However, volunteering boosts institutional trust because volunteers get in touch with a political and administrative system that supports and interacts with the voluntary sector. This applies particularly to voluntary organizations in culture, sports, and recreation. In contrast, in an institutional context with elements of clientelism and corruption, as in the case of the Czech Republic, there is no positive effect on institutional trust. However, the level of general social trust is low and the collaborative experience of volunteering can generate social trust. This applies particularly to voluntary organizations that are not associated with the established political culture.