While company law makes great efforts to maintain the separation of different legal entities, other areas of law increasingly emphasise the common responsibility of corporate groups. One of the fields shaping this emerging principle is competition law, where focusing on the whole group rather than its individual members is increasingly becoming the norm. But this approach is still far from being uniformly accepted. While EU competition law is pushing ahead, US antitrust law is said to take a rather critical stance. Against this background, this chapter examines the functions performed by a unitary perspective on corporate groups. The main goal is to show that at least three important functions must be distinguished in EU competition law, each of which has its own implications. Only when these are properly understood can it be determined where the group perspective is appropriate and where it is not. This is shown by the example of current discussions, for example, on the liability of sister companies and on possible applications in the area of liability for damages. Finally, the analysis in this chapter also aims to contribute to a better understanding of the different approaches in EU and US competition law.