Cohabitors and married people who cohabited before marriage have higher risks of union dissolution than people who married without prior cohabitation. However, these differences in union stability vary markedly between countries. We hypothesize that the impact of cohabitation on union stability depends on how far cohabitation has diffused within a society. We test this hypothesis with data from 16 European countries. The results support our hypothesis: former cohabitors run a higher risk of union dissolution than people who married without prior cohabitation only in societies in which cohabitation is a small minority or a large majority phenomenon.