  Although the theoretical study of very low metallicity (Z) and metal-free
stars is not new, their importance has recently greatly increased since two
related fields have been developing rapidly. The first is cosmological
simulations of the formation of the first stars and of the reionisation period.
The second is the observations of extremely metal poor stars. In this paper, we
present pre-supernova evolution models of massive rotating stars at very low Z
(Z=1e-8) and at Z=0. Rotation has a strong impact on mass loss and
nucleosynthesis. Models reaching break-up velocities lose up to ten percents of
their initial mass. In very low Z models, rotational and convective mixing
enhances significantly the surface content in carbon, nitrogen and oxygen (CNO)
when the star becomes a red supergiant. This induces a strong mass loss for
stars more massive than about 60 solar masses. Our models predict type Ib,c
supernovae and gamma-ray bursts at very low Z. Rotational mixing also induces a
large production of CNO elements, in particular of primary nitrogen. The
stellar wind chemical composition is compatible with the most metal-poor star
know to date, HE 1327-2326, for CNO elements. Our models reproduce the early
evolution of nitrogen in the Milky Way.
