This is the technical report accompanying the dataset of the Unions in Context (UNICON) study. The UNICON study is a web-based probability survey among same-sex and mixed-sex couples conducted in 20 Dutch municipalities in 2016. The main objective driving this project was the need for data on same-sex couples and their children which are not biased by convenience recruitment strategies. DESIGN The probability sample was drawn by means of a sampling frame based on population registers including also those couples who are cohabiting without being in an officially registered union (marriage or civil partnership). The sampling design also specifically aimed at capturing the complex realities regarding parenthood in same-sex couples by selecting same-sex headed families not on the basis of officially registered parental status but based on the presence of children in the household. The final dataset includes responses from 600 same-sex couple households (of which 140 with children) and about 320 mixed-sex couple households (of which 230 with children). CORE CHALLENGES IN THE FIELD The UNICON data address five core challenges faced when studying same-sex couples and families quantitatively. The study: (1) purposefully includes same-sex couples and families in the sampling frame (2) uses a random sample that allows for generalization (3) oversamples same-sex couples to achieve a large number of observations (4) includes a suitable comparison group of mixed-sex couples (5) covers a wide range of substantive topics both specific to same-sex couples and general topics