This book explores how the EU's enforcement of competition law has moved from centralisation to decentralisation over the years, with the National Competition Authorities embracing more enforcement powers. At the same time, harmonisation has been employed as a solution to ensure that the enforcement of EU competition rules is not weakened and the internal market remains a level playing field. While employing a comparative law argument, the book, accordingly, analyses the need for harmonisation throughout the different stages of development of the EU's competition law enforcement (save Merger control and State Aid), the underlying rationale, and the extent to which comparative studies have been undertaken to facilitate the harmonisation process from an historical perspective. It also covers the Directives, such as the Antitrust Damages Directive and the ECN+ Directive. Investigating both public and private enforcement, it also examines the travaux préparatoires for the enforcement legislation in order to discover the drafters' intent. The book addresses the European and the Member States' perspectives, namely, the Central and Eastern European (CEE) countries, as harmonisation proceeds through dialogue and cooperation between the two levels. Lastly, it explores the extent to which harmonisation of the competition law enforcement framework has been accepted and implemented in the Member States' legal systems, or has led to the fragmentation of the national systems of the CEE countries.