Oxytocin (OT) is a widely studied hormone since it plays a central role in shaping and regulating many endogenous and behavioural mechanisms important for social behaviour in mammals. The avian OT, formerly called Mesotocin (MT) appears to have a similar influence. However, its function and control mechanisms in birds are still unclear as research on avian OT was scarce and only recently received more attention thanks to the development of novel and less-invasive methods. OT in birds is associated with parental care and social behaviours such as mating, nest-building and chick-rearing, as well as physiological dynamics such as water balance, oviposition and diuresis. In this review, we try to describe the role and control mechanisms of OT in regulating behaviour and physiology in birds, summarizing information from over 60 years of literature. First, we will elucidate the state-of-the-art findings about OT evolution across taxa and report recent discussions regarding nomenclature. Then, we will describe the hormone action in the central and peripheral system, including its behavioural influences and its interaction with another closely related peptide, vasotocin. To conclude, we will describe novel methods used to quantify OT, underlining their pros and their cons.