The tendency of members of many ethno-religious groups to marry within their group has been considered evidence for the persistent role of ascription in modern society. What is the role of the family of origin in this process? To answer this question, we study the marriage choices of Jews in the Netherlands, using a unique dataset and a novel analytical approach (i.e., multilevel analyses of sibling-data). Our models show that almost a third of the variation in Jewish endogamy can be attributed to a common family factor. Measured indicators of family background point to two underlying mechanisms: the intergenerational transmission of ethnic identities and the intergenerational provision of endogamous meeting and mating opportunities. Together, these mechanisms explain 75 percent of the total family influence. The degree to which members of ethnic and religious groups marry within rather than outside their group is often viewed as an indicator of the strength of ascription in society. Studies on marriage choice have shown that most forms of ethnic and religious intermarriage have become more common over time (Kalmijn 1991; Lieberson and Waters 1988), in line with the frequently made claim that the importance of ascription in society has declined (Blau and Duncan 1967). It has also been recognized, however, that this transition is far from complete. Ethno-religious boundaries in society may have become weaker, but they have certainly not disappeared. Most of the interest of marriage researchers has focused on new immigrant groups and their descendants, groups that have increased in size and that have become increasingly important in debates about integration and multiculturalism. Older ethno-religious groups, groups that are less visible, and groups that have declined in size have received comparatively little attention. This is particularly true for the position of Jewish persons in Europe. We re-examine the role of ascription in contemporary society by analyzing the marriage choices of Jews in the Netherlands after the Second World War. Using a unique data set and a novel analytical approach – multilevel analyses of siblings – we examine to what extent family background plays a role in explaining Jewish endogamy. Although it is often assumed that ethno-religious endogamy is an indicator of ascription, the degree to which this is true depends on how important the family of origin is in this respect. In other words, if choices are largely made within the group and the family factor is important, ethnicity is largely ascribed. If choices are endogamous but the parents play no role, choices are more individual in nature and ethnicity becomes ‘achieved’ rather than ‘ascribed.’ Under the assumption that one’s ethnic background is not visible in day-to-day encounters, people may choose their ethnic identity out of the ethnic options they have (Waters 1990). We argue that the importance of ascription in society should not only be assessed by measuring ethno-religious marriage boundaries, but also by assessing the extent to which ethno-religious endogamy is dependent on family background influences.