The first galaxies: clues from element abundances

It has recently become possible to measure directly the abundances of sever al chemical elements in a variety of environments at redshifts up to z simi lar or equal to 5. In this review I summarize the latest observations of Ly man-break galaxies, damped Ly alpha systems and the Ly alpha forest with a view to uncovering any clues that these data may offer to the first episode s of star formation. The picture that is emerging is one in which the Unive rse at z = 3 already included many of the components of today's galaxies; e ven at these early times we see evidence for Populations I and II stars, wh ile the 'smoking gun' for Population III objects may be hidden in the chemi cal composition of the lowest density regions of the intergalactic medium, yet to be deciphered.