  The horizon for studies of element abundances has expanded dramatically in
the last ten years. Once the domain of astronomers concerned chiefly with stars
and nearby galaxies, this field has now become a key component of observational
cosmology, as technological advances have made it possible to measure the
abundances of several chemical elements in a variety of environments at
redshifts up to z = 4, when the universe was in its infancy. In this series of
lectures I summarise current knowledge on the chemical make-up of distant
galaxies observed directly in their starlight, and of interstellar and
intergalactic gas seen in absorption against the spectra of bright background
sources. The picture which is emerging is one where the universe at z = 3
already included many of the constituents of today's galaxies-even at these
early times we see evidence for Population I and II stars, while the `smoking
gun' for Population III objects may be hidden in the chemical composition of
the lowest density regions of the intergalactic medium, yet to be deciphered.

Astrophysics