Previous research has demonstrated that parental socio-economic status (SES) is an important determinant of the timing of entry into a first co-residential union. Whilst the majority of existing studies found that young adults from high-SES families delay their first union compared with those from lower-SES backgrounds, all these studies were conducted within a single country. This study examines the link between parental SES and the timing and type of first union for 25 European countries participating in the European Social Survey Round 3 (2006/2007). Results from two-step meta-analytical models indicate that in almost all countries young adults from advantaged backgrounds delay their entry into a first union. This delaying effect of parental SES is stronger if young adults marry directly than if they enter their first union via unmarried cohabitation. The impact of parental SES is only partly mediated by an individual’s own education. The strength of the link between parental SES and union formation varies between countries: the delaying impact of parental SES is weakest in those Northern and Western European countries that are most advanced in the Second Demographic Transition. However, after controlling for individual education, the cross-national variation in the link between parental SES and union formation disappears.