Sergio Simón-Díaz is Staff Researcher at the Instituto de Astrofísica de Canarias, Tenerife. He is mainly involved in the observation and analysis of massive stars and he has authored more than a hundred refereed papers. At present he is leading the IACOB project, a long-term observational project aimed at providing an overview of the main physical properties of Galactic massive O- and B-type stars to be used to improve our current understanding of the current theories of stellar atmospheres, winds, interiors and evolution of massive stars.