The extent and implications of cohabitation and marriage among US welfare recipients are investigated. An analysis of 4 data sets shows significant numbers of cohabitors among recipients of AFDC. An even more surprising finding is the large number of married women on welfare. The results of a telephone survey of state AFDC agencies is also reported. The survey was conducted to determine state rules governing cohabitation and marriage. The survey results indicate that, in a number of respects, AFDC rules encourage cohabitation. Finally an analysis of the impact of AFDC rules on cohabitation, marriage, and single motherhood is conducted, and weak evidence is found in support of incentives to cohabit. (Author abstract)