Halo stars can be distinguished from disk stars by their lower metallicity
and their very different kinematics. They are generally assumed to be old,
and would be the first witnesses of the formation of our Galaxy. The
analysis of their surface composition would allow to trace the primordial
nucleosynthetic processes. It is thus particularly important to know
the details of their abundances and to compare them to the Sun and other
The low metallicity of the halo stars is comparable to that of the globular clusters, which form another conspicuous component of the galactic halo. In a near future, the spectroscopic observations will allow to study in detail the chemical composition of these clusters and to compare them with the field halo stars.