This book contains a comparative study into defence rights during administrative investigations in the context of administrative law. This book concentrates on the work of the European Anti-Fraud Office, OLAF, which ordered this study. Since administrative law is about decisionmaking, defence rights are not the primary focus of administrative lawyers. They direct their attention to the rules and principles that guide the decision-making process of administrative offices and the legal protection against such legal acts. Defence rights are present in the administrative law enforcement context, but their form often differs from that of criminal law enforcement. This study contains an inventory of these defence rights in administrative law in Switzerland and 6 EU Member States: England & Wales, Germany, Italy, the Netherlands, Romania and Sweden. It presents the general and comparative aspects of the defence rights as recognized by the EU courts and the European Court for Human Rights, as well as in the different administrative law systems. On the basis of this comparison, recommendations aimed at adapting EU Regulations and OLAF working methods are presented.