  Big Bang nucleosynthesis produces only light elements and the very first
generation stars are thus formed from metal-free clouds. They start the
production of heavy elements during their life, and enrich the interstellar
medium through their explosive death. Stellar evolution models show that the
treatment of rotation has important effects on the evolution of those
metal-free stars: for example, rotating models produce up to five orders of
magnitude more primary nitrogen than non rotating models, due to internal
mixing. This will have an impact in the composition of the second generation
stars, some of which may now be observed in the Galactic halo. In the case
Population III stars were very massive and would end up as direct black holes,
rotation again have an interesting effect of enhancing mass loss through
centrifugal force and surface enrichment. CNO composition patterns observed in
ultra metal-poor halo stars may be explained by a 'wind only' contribution.
