As a result of recent changes in marriage behaviour, it is no longer possible to study this subject solely by using information from vital registration and censuses. For instance, in France two-thirds of first unions are not legal marriages, and one-third of first births take place outside marriage. It is, therefore, necessary to collect individual detailed marital histories, such as those that were obtained in the Enquiry on Family Life towards the end of 1985. In the present paper, we consider the conditions under which first unions take place (type of union and age of parties), as well as their eventual outcome (marriage or separation). Successive cohorts of first unions after 1968 have experienced different histories: the transition from the traditional model to the present one has been characterized by discontinuities. In the most recent cohorts (1980-82), marriage is still the most frequent outcome of first unions that began outside marriage (50 per cent marry within the first three years of the union); pre-marital cohabitation does not appear to have affected the stability of marriage, and altogether one-fifth of first unions are broken within ten years.