While company law makes great efforts to maintain the separation of different legal entities, other areas of law strive in the opposite direction. In recent times, there has been a new emphasis on the common responsibility of corporate groups, especially when they are large and powerful. One of the fields that shape this emerging principle is competition law. Focusing on the whole group and not on its individual members is increasingly becoming the norm here. But it 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 book chapter examines the functions performed by a unitary perspective on corporate groups. A special focus is on the calcu-lation of fines, an issue that is currently the subject of many court disputes in Europe. It is argued that the best approach is usually to consider the whole group as it exists at the time of the prohi-bition decision, even if there have been changes in the corporate structure in the past. Questions of liability are also examined in detail. One of the main aims of the chapter is to raise awareness of how different the functions of a unitary perspective on corporate groups are and how im-portant this insight is for the conclusions that can be drawn.