  Massive stars played a key role in the early evolution of the Universe. They
formed with the first halos and started the re-ionisation. It is therefore very
important to understand their evolution. In this review, we first recall the
effect of metallicity (Z) on the evolution of massive stars. We then describe
the strong impact of rotation induced mixing and mass loss at very low Z. The
strong mixing leads to a significant production of primary nitrogen 14, carbon
13 and neon 22. Mass loss during the red supergiant stage allows the production
of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs)
down to almost Z=0 for stars more massive than 60 solar masses. Galactic
chemical evolution models calculated with models of rotating stars better
reproduce the early evolution of N/O, C/O and C12/C13. Finally, the impact of
magnetic fields is discussed in the context of GRBs.
