An essential tool in the social sciences, gender can be crossed with generation in the demographic sense. Because age is always gendered: the periods of life are different depending on whether they take place in the shadow of the feminine or the masculine. This special issue is dedicated to "boyness", i.e. the learning of the masculine in childhood. Whether they grew up in ancient Rome, Greek cities, medieval towns, modern Germany or Third Republic France, millions of boys have been educated and socialized within the codes of masculinity, which they have acquired – or not.