The careful categorisation of conduct is one of the fundamental tasks that courts must perform when interpreting and applying competition law provisions. This contribution makes several points in relation to this idea. To begin with, it defines and explains the pivotal role of categories in the system. It focuses on Articles 101 and 102 TFEU, but the lessons drawn could be easily extended to other areas of EU law Second, it discusses the two main approaches that could be followed to the categorisation of conduct: one that is formal and another one that is substantive (or substance-based). It notes, in this regard, that, economic analysis is not only not inimical to this exercise but can greatly contribute to the creation of sound categories. The piece moves, third, to the analysis of the Court’s approach and of the techniques it uses to address and correct frictions and inconsistencies over time.