The evolution of massive and very massive stars in clusters

The present paper reviews massive star (initial mass ⩽ 120 M⊙) and very massive star (initial mass > 120 M⊙) evolution. I will focus on evolutionary facts and questions that may critically affect predictions of population and spectral synthesis of starburst regions. We discuss(a) the effects of ever-lasting factor 2 or more uncertainty in the stellar wind mass loss rates;(b) the effects of rotation;(c) the effects of binaries;(d) the effects of stellar dynamics in dense cluster cores on the formation and evolution of very massive stars.