Olivier Gascuel studied mathematics and completed a PhD in computer science. He started working on bioinformatics by the end of the 1980’s, at the very beginning of the genomic era and of the rapid development of interactions between mathematicians, computer scientists and molecular biologists. His early interests were in sequence analysis and protein structure prediction, using machine learning approaches. Since the mid-1990’s, Olivier Gascuel has concentrated on evolution and phylogenetics, with particular focus on the mathematical and computational tools and concepts. He recently became the head of the new Center for Bioinformatics, Biostatistics and Integrative Biology (C3BI) of the Pasteur Institute at Paris, and turned part of his activities toward pathogens and epidemiology. He is an associate editor of Systematic Biology and belongs to the editorial board of several bioinformatics journals. He has published more than 150 papers and book chapters, and authored several widely used computer programs in phylogenetics and bioinformatics such as BioNJ and PhyML.