This paper adds to our limited knowledge of racial and ethnic variation in union formation by describing and analyzing the first unions of mainland Puerto Rican women. Retrospective history data show that Puerto Ricans have shared in the post-1970 shift toward cohabitation. Puerto Rican women, however, are much more likely to enter informal first unions than the general population, and have a low propensity to transform informal unions into legal marriages. The paper examines the influence of family background and current activities on union timing and type. The relationship between partner attributes and the choice between formal and informal coupling is also considered.