Abstract: Very massive stars (VMS) with masses over 100 times the mass of the Sun are dominant sources of ionising radiation, which may have been the key source of cosmic re-ionisation. The prime difference between VMS in our local Universe and those in the Early Universe is their metallicity (Z).  In this talk, I will discuss how this is anticipated to change the stellar upper mass limit, massive star formation, wind mass loss, stellar evolution, as well as final black hole masses.