Résumé : The EORTC Infectious Disease Group (IDG) and its forerunners, the International Antimicrobial Therapy Cooperative Group (IATCG) and the Invasive Fungal Infection Group (IFIG), have helped drive and develop clinical practice in the management of bacterial and fungal infectious diseases. Besides undertaking seminal studies, the group in its various forms has played a key role in understanding the nature and management of the infectious complications that arise during the treatment of cancer, particularly hematological malignancies. The IATCG was also instrumental in setting the stage for large randomized controlled trials to address therapies for dealing with infections that developed during neutropenia. The three most important achievements of the group were in finding a rational basis for managing bacterial and fungal infections, the establishment of disease definitions, and the development of the guidelines. © 2012 European Organisation for Research and Treatment of Cancer.