  The chemical composition of high-redshift galaxies is an important property
that gives clues to their past history and future evolution. Measuring
abundances in distant galaxies with current techniques is often a challenge,
and the canonical metallicity indicators can often not be applied. I discuss
currently available metallicity indicators based on stellar and interstellar
absorption and emission lines, and assess their limitations and systematic
uncertainties. Recent studies suggest that star-forming galaxies at redshift
around 3 have heavy-element abundances already close to solar, in agreement
with predictions from cosmological models.
