There are many books on the medieval nobility in general, and kinship in particular, but very little has been written on noble siblings. Overwhelmingly, scholarship has concentrated on intergenerational and, more recently, conjugal relations to understand noble kinship. This is at least partly due to a scholarly tradition with which Jonathan R. Lyon critically engages in his monograph on Princely Brothers and Sisters: Duby’s version of the so-called Schmid/Duby thesis is still widely influential, if only because it keeps on being refuted. Famously, Duby argued for a relatively sudden change towards patrilineal kinship structures in the eleventh century. For medieval France, a large number of regional studies have critically engaged with this model (e.g. Barthélemy, Bouchard, Evergates, Livingstone, Thompson, White). In addition, Jack Goody inspired a number of studies taking a very different approach but on the whole coming to similar conclusions. Both traditions have provided ample evidence against the mutation lignagère in general and the supposed rise of primogeniture in particular.