The protection of fundamental rights and procedural guarantees in administrative investigations conducted by the European Anti-Fraud Office (OLAF) has constantly evolved since its creation in 1999. First, the catalogue of procedural rights and guarantees embedded in the successive regulations governing the conduct of OLAF’s investigations was significantly expanded. Second, the existing mechanisms to ensure their protection were reinforced by the creation of the new function of the Controller of procedural guarantees and a new complaints mechanism. As a result, the legal framework under which OLAF operates at present is significantly more protective of fundamental rights and procedural guarantees than it was 25 years ago. This article sheds light on these two key developments: the progressive codification of fundamental rights and procedural guarantees applicable to OLAF’s investigations and the reinforcement of their protection by the creation of the new Controller and the new complaints mechanism.

The article examines the evolution of the European Anti-Fraud Office over the past 25 years from its establishment in 1999 to its current role as a pivotal player in the fight against fraud affecting the EU’s financial interests. It starts by tracing OLAF's origins to its predecessor, the Unit for the Coordination of Fraud Prevention, and the circumstances surrounding OLAF’s creation as a response to major corruption scandals. The article goes on to analyse the legal framework underpinning OLAF’s mandate, in particular Regulation No. 883/2013 and Directive 2017/1371 on the fight against fraud to the Union’s financial interests by means of criminal law, which expanded OLAF's scope and facilitated its cooperation with the European Public Prosecutor’s Office. Furthermore, OLAF's evolving relationship with the EPPO is explored and significant case law that has shaped OLAF’s investigative powers and procedural safeguards highlighted. The article concludes by reflecting on OLAF’s achievements and the challenges it faces in combating fraud in an increasingly complex and multifaceted international financial landscape.