EU enforcement agencies are on the rise, entrusted with investigating breaches of EU law. What are the implications for legal practice of their increasing prominence? This books explores this pertinent question from a comparative perspective. Looking at issues of accountability and legitimacy, it sets out the perimeters on the agencies. Moving beyond the constitutional realm, it examines procedural questions such as admissibility of evidence. Given the very real implications of the agencies' investigations, this book will appeal to practitioners and scholars, in fields from criminal law to competition and banking law.