The European Anti-Fraud Office was created 25 years ago, in 1999, to fight fraud, corruption, and any other illegal activities affecting the EU budget. While there are several anti-fraud actors at EU level, OLAF is unique with regard to its international activities. In particular, OLAF is mandated to conduct investigative activities directly on territory outside the EU. Against this background, the article traces the evolution of the EU legal framework for OLAF’s international investigations and the parallel development of OLAF’s international relations in practice. The analysis of OLAF’s engagement with international partners focuses on several key activities of the Office to protect EU funds abroad, especially negotiating anti-fraud provisions in international instruments, concluding administrative cooperation arrangements with non-EU countries and international organisations, and building networks of partners around the globe. Looking back at the past quarter of a century, the article demonstrates that many features which are hallmarks of OLAF’s international relations today can be traced back to the early years of the Office. The article also shows how these practices have grown and matured over time.