Prof. Stefanelli has been one of the most influential researchers in medical informatics.He was one of the founders of the European Society for Artificial Intelligence in Medicine, which started its activity in Pavia in 1985 with its first European meeting. He strictly collaborated with IMIA. After having been member of MedinfoSPCs, his influential role within IMIA has led him to be appointed as SPC chair of Medinfo 2004 together with Casimir Kulikowski. Medinfo 2004 is widely recognized as one the best IMIA conferences. He always fostered IMIA activities and worked with IMIA affiliated societies, including AMIA and EFMI. He has been the first Italian to be elected Fellow of the American College of Medical Informatics. He coordinated several research projects funded by the European Commission and actively collaborated with many medical informatics laboratories in the world. He has been a member of the editorial board of prestigious international journals, comprising the Journal of Biomedical Informatics, the International Journal of Medical Informatics, Artificial Intelligence in Medicine, and Methods of Information in Medicine. A brief synthesis of his scientific career starts in the ‘70s, when he gave important contributions to the mathematical modelling of erythropoiesis, using both quantitative methods and qualitative simulation methods, with applications to the diagnosis of anaemia. His specific interest to the problem of diagnostic reasoning motivated him to start a new research activity in the area of decision support systems and artificial intelligence in medicine. After a visit to the Casimir Kulikowski’s labs at the Rutgers University, Mario Stefanelli opened a Medical Informatics Labs at the University of Pavia, which soon became a leading laboratory worldwide.