In order to improve animal welfare, a growing number of calves, heifers and dairy cows are reared in loose housing systems. However, regrouping unfamiliar animals may result in aggressive interactions and distress. Increased knowledge about grouping and social integration would make it possible to develop effective management techniques that reduce the amount of problems occurring during social integration of cattle. The aim of this paper is to review recent literature on social integration of calves, heifers and cows and how this is influenced by early social environment, group size, introduction method and competition level. Grouping unfamiliar animals is found to increased aggression, social stress, locomotion behaviour and to have negative effects on feed intake and milk yield. Problems related to social integration are normally higher for the introduced animals than the resident animals. Previous social experience, number of animals that are mixed and the group composition are important factors that can influence social integration. Calves reared in groups are more social confident and show less fear than calves reared in single boxes or in isolation. Repeated grouping seem to accustom the animals to these procedures.