New models of massive stars have been calculated as a part of a project aimed at the construction of an extended grid of stellar tracks for several metallicities, covering all the main evolutionary phases of low, intermediate and massive stars, with updated physics. After a brief description of the input physics, we discuss the properties of the stellar content of young clusters as a function of the age and metal content, in the light of the new evolutionary models. Furthermore we review the global properties of the observed HR diagrams of massive stars in the Solar Vicinity and LMC and discuss the major points of disagreement that emerge from their comparison with those artificially generated from our database of evolutionary tracks.