Although cohabitation and childbearing within cohabitation have increased in Europe over recent decades, the variation across Europe remains remarkably wide. Most studies on union formation have not explicitly addressed the role of state policies in the development of cohabitation or discussed how countries have responded to changes in union formation by passing legislation. Here we discuss historical and theoretical issues relevant to the relationship between state policies and union formation and describe policies relating to cohabitation and marriage in nine Western European countries. Drawing on secondary sources and legal documents, we examine the quantity of regulations that mention cohabitation and the approach to cohabitation in 19 policy dimensions. We then place the countries along a continuum, from those that have equalized cohabitation and marriage to those that only regulate marriage. As a whole, this overview raises questions about the changing institution of marriage, as well as the increasing institutionalization of cohabitation.