Objective: To understand levels of support for differences between families in terms of sexuality and mode of family formation across three countries. Background: Previous research has found that attitudes towards family diversity continue to improve over time, although differences remain. Methods: Subjects were 1605 people living in Australia, the United Kingdom or the United States who completed a questionnaire which sought to explore levels of support for a diverse range of family forms and modes of family formation. Results: Religiosity, political leanings and beliefs about the importance of genetic relatedness were all correlated with level of support. Gender of participant was a predictor of level of support. Cluster analysis indicated three clusters (unsupportive, neutral and supportive) for level of support, for which both sexuality and parent status were predictors. Conclusion: Findings highlight the normative status of reproductive heterosex, and demonstrate the considerable value accorded to genetic relatedness.