Who is bound by the competition rules in the EC Treaty? Article 81 EC applies to agreements and concerted practices between undertakings and to decisions of associations of undertakings; two addressees are specified: (a) undertakings and (b) associations of undertakings. This paper is mainly concerned with the meaning of (a) undertaking. As noted by Advocate General Jacobs, ‘the concept of “undertaking” serves a dual purpose in the system of Article [81]. On the one hand—and this function is more obvious—it makes it possible to determine the categories of actors to which the competition rules apply. . . . On the other hand, it serves to establish the entity to which a certain behaviour is attributable’.