I review the most widely used methods of determining chemical
abundances in galaxies at 1≲ z ≲ 3, including emission and
absorption line techniques (including a brief discussion of Damped
Lyman Alpha systems). Most star-forming galaxies at these redshifts
show significant enrichment, with ~1/3 solar to ~solar
metallicities. They are overluminous for their metallicities compared
to local galaxies, and the mass-metallicity relation at z ~ 2 is
offset to lower metallicities compared to the local relation. Metals
are also seen in the IGM at these redshifts, most likely from
galactic-scale outflows in the galaxies themselves.