Farm animals develop an important social network with intra- and interspecific partners, including humans. In some cases this can lead to strong emotional bonds indicating the existence of attachment. There is no doubt that a better understanding of the mechanisms of attachment will benefit animal welfare. As a model, the sheep is well known to develop various forms of social attachment (mothers towards young, lambs towards siblings). The relationship they can develop with humans is much less understood. In this review we outline features and mechanisms that participate in the development and the expression of intra- and interspecific social attachment in lambs. Behavioural tests comparing responses towards a presumed attachment figure with those directed towards unfamiliar or familiar conspecifics demonstrate that lambs do search specifically the proximity of their mother, sibling or human caretaker. Differential emotional responses in the presence (calmness) or the absence of the partner (agitation) are also expressed. However, a relationship with a human takes place more easily when lambs are reared without their primary attachment figure, the mother. Human- lamb attachment is then facilitated by positive social contacts (stroking) provided by a specific caretaker. In the case of attachment with the mother, suckling is the main reward. Positive social contacts including stroking or suckling activate similar brain regions and trigger a release of oxytocin, a neuropeptide known to play a key role in prosocial behaviours. Recent evidence even supports a role for oxytocin in the development of filial attachment. In conclusion, lambs develop intra- and interspecific attachment but not in a concomitant manner as the presence of the mother strongly reduces the lamb’s motivation to interact with a human. However, under artificial rearing conditions the human becomes a salient attachment figure which may facilitate the management of lambs on farm.