  A galaxy's metallicity provides a record of star formation, gas accretion,
and gas outflow, and is therefore one of the most informative measurements that
can be made at high redshift. It is also one of the most difficult. I review
methods of determining chemical abundances in distant star-forming galaxies,
and summarize results for galaxies at 1<z<3. I then focus on the
mass-metallicity relation, its evolution with redshift, and its uses in
constraining inflows and outflows of gas, and conclude with a brief discussion
of future prospects for metallicity measurements at high redshift.
