Our review of extrapair paternity in birds is published today in Molecular Ecology and can be accessed here. The paper, written by Lyanne Brouwer and myself, is an update on the last review that I published on the subject in 2002. There are now over 30 years of molecular data on the incidence of extrapair offspring in socially monogamous species and we present an overview of over 500 studies focused on over 300 species. Overall, in around three quarters of socially monogamous species, some evidence of infidelity has been found. In the species in which it occurs about one fifth of all offspring are fathered by an extrapair sire, and therefore not by the social male who is investing in their care. We also demonstrate that the incidence of extrapair paternity is more likely to occur in some avian families, being particularly prevalent in passerines, and rarer, or completely absent in families that are long-lived, such as owls, or seabirds.