This article discusses examples of inheritance law reform in different countries all dealing with the current transformations of family structures. The first part analyses discussions in US and English law on the intestate share of spouses in second or subsequent marriages in relation to the share of the children of the deceased. The second part summarises the author’s own suggestions for the reform of Swiss inheritance law having regard to empirical social science literature on changing family realities. The examples from the three legal systems reveal that, although the relationship between the “Is” and the “Ought” is fundamentally different depending on the legal tradition, in both the Anglo-American and the continental European context the use of social science knowledge in inheritance law reform is currently predominantly based on a model of social science as a mere adjunct of legal studies. The author argues in the third part of the article that, especially for the complex situation of blended families, genuine transdisciplinary research could be a promising means of developing innovative solutions for inheritance law reform.