It is well-known that married and cohabiting women differ in labour supply. But we know very little about the causes of this difference. Is it due to differences in characteristics, like age, presence and ages of children, own net wage rate, and net income of the partner? Or is it a difference in behaviour that – even after controlling for variation in characteristics – is the basic cause? In this article we try to answer these questions for Dutch married and cohabiting women. We use data of national surveys by Statistics Netherlands for 1989 and 1998. This also allows us to investigate whether there have been important changes in the last decade. Because we are able to compare the results with those of an analogous analysis that two of the authors did on similar Dutch data for 1981 we are able to draw conclusions about changes that took place over the last twenty years. The results show that the massive growth in female labour force participation is especially due to the growth in participation by married women. A slight decrease in labour market participation of cohabiting women can be observed in the last decade. This seems to be the result of cohabitation becoming more normal, including cohabitation when there are young children in the household.
