Since the end of the 1980s, the ways people live together in a relationship have changed significantly. Marriage under the community of property regime was the dominant system for couples that formed between 1980 and 1992, but this traditional form of partnership was not the most common among couples that formed between 1998 and 2010, partly due to the decline in marriages but also, for married couples, due to the increase in the adoption of the separation of property regime. This trend can be explained in two ways. On the one hand the increased risk of divorce can alter the behaviour of couples with given characteristics. On the other hand, these characteristics of couples also evolved over the period, whether in terms of estate, inequalities between spouses, or the labour market offering for women. We break down the changes in the instances of marriage and of the adoption of the separation of property regime in order to determine which factors seem to explain the trends observed in the way partners live together. We show that the drop in marriages is mainly explained by a change in the behaviour of couples, particularly the fact that the link between estate and marriage has weakened over the years while the commonness of divorce has made it easier to (re)marry. The growth in instances of separation of property is principally explained by the changes in characteristics of couples, particularly the increase in household assets and in inequalities between spouses.