Mismatches between the evolutionary biology of the sow and current commercial production systems give rise to welfare challenges of stereotyped behaviour development in confined systems and aggression in group housing systems. This chapter describes the welfare issues associated with individual confinement systems and examines the nature and significance of stereotyped behaviour in gestating sows. The chapter addresses the issue of hunger in the pregnant sow and drivers to adopt group housing systems for pregnant sows. The chapter has a particular focus on the importance of social organisation in sows and looks in detail at the relationship between aggression in stable groups and the method of feed provision available. Finally, the chapter examines sows in extensive systems and looks ahead to future research trends in this area, providing extensive suggestions for further reading.