„It is well established that keeping pregnant sows in individual stalls impairs their welfare. Based on this reason the EU Council Directive001/88/EC prohibits individual stalls for pregnant sows from January 1, 2013. The present review focuses on main problems and possible solutions for group housing of pregnant sows in relation to their welfare. Possible problems in group housing are the impact of stress on reproductive performance of sows in group housing systems due to mixing of unfamiliar sows, aggression in newly grouped sows, aggression between sows at feeding. The review concludes with recommendations how housing systems should be designed and managed to minimize aggression and thus to meet the welfare needs of sows through maintaining stable groups with minimal mixing of unfamiliar sows.“