The most important features of the behaviour of sheep are their marked sociality and the formation of a bond between mother and young. Sheep show a strong need to stay with their flock mates and become very distressed when isolated. Under farm conditions the social environment is mainly controlled by humans, and sheep are usually maintained in single-sex groups of similar age or size, the main exceptions being male–female groups at mating and the mother–young dyad. Separating lambs from their mother at an early age and rearing them with artificial milk is also a frequent practice. This chapter examines the importance of understanding sheep sociality, sexuality, mother–young bonding to sheep welfare, as well as describing the impact of environmental conditions on sheep behaviour.