The neuropeptide arginine vasopressin (AVP) is arguably among the most potent regulators of social behaviors in mammals identified to date. However, only the related neuropeptide oxytocin (OXT) has been shown to promote maternal behavior. Here, we assess the role of AVP in maternal care, in particular in arched back nursing, pup retrieval, and pup contact by using complementary pharmacological and genetic approaches. Also, experiments were performed in rat dams with differences in trait anxiety, i.e., rats bred for either high (HAB) or low (LAB) anxiety-related behavior as well as nonselected (NAB) dams. Viral vector-mediated up-regulation of AVP V1a receptors (AVP-Rs) within the medial preoptic area of lactating NAB rats and chronic central AVP treatment of NAB and LAB dams improved, whereas local blockade of AVP-R expression by means of antisense oligodeoxynucleotides or central AVP-R antagonism impaired, maternal care in NAB dams. Also, in HAB rats with a genetically determined elevated brain AVP activity, intrinsically high levels of maternal care were reversed by blockade of AVP-R actions. Treatment-induced impairment of AVP-mediated maternal behavior increased adult emotionality and impaired social interactions in male offspring of NAB dams. These findings provide direct evidence for an essential and highly potent role of brain AVP in promoting maternal behavior, which seems to be independent of the dam's trait anxiety.