Hamilton's principle of inclusive fitness implies that reproductive altruism can evolve, because individuals can pass on genes not only through their own offspring, but also through the offspring of their relatives. Social insects are spectacular examples of how some individuals may be selected to forgo reproduction and instead help others reproduce. Social Hymenoptera are also special because relatedness patterns within families can be asymmetrical, so that optimal sex-ratios, preferred male parentage or preferred mating frequencies become objects of reproductive conflict. The now extensive inclusive fitness theory provides precise qualitative predictions with respect to the emergence of such conflicts. Recent advances in the power of genetic markers applied to resolve family structure in insect societies have brought about a series of studies that have tested these predictions. In support of kin selection as a major evolutionary force, the results suggest that workers frequently control sex allocation. However, the very establishment of such worker control has made new conflicts come to light, between mothers and fathers and between adult individuals and brood. Evidence for these conflicts is only just beginning to be gathered. Recent studies tend to include issues such as 'information' and 'power' (i.e. the ability to perceive signals and the opportunity to act upon this information), and to address selection for selfishness at the individual level with costs of social disruption at the colony level.