This chapter deals with the European Union law on competition and mergers, with emphasis on the provisions of Articles 101 and 102 of the TFEU. The role of markets is to coordinate supply and demand. EU competition law is applied to address situations in which firms are able to distort the ability of markets to coordinate supply and demand, such problems arising when firms are able to aquire or exercise power over the market. A number ways in which problems of market power manifest themselves and the ways in which EU competition law can be, and has been, marshalled to address those problems are the subject of this chapter. This chapter considers the idea of a market and the absence of competitive constraints, before consider unilateral and collusive behaviour giving rise to or exploiting market power. Finally, it considers the EU Merger Regulation as a primary instrument for regulating the competitive consequences of durable changes in market structure.