Families are regulated not only in the ‘primary’ family law of Civil Codes, but also in ‘secondary’ family law, i.e., rules relating to families in social, tax, administrative, criminal and other laws. This research line addresses the gaps and inconsistencies between primary and secondary family law, with a focus on the negative assumptions in secondary family law towards families who do not use the family institutions of primary family law (unmarried cohabitation; de facto parents etc.)