  The evolution of the content of heavy elements in galaxies, the relative
chemical abundances, their spatial distribution, and how these scale with
various galactic properties, provide unique information on the galactic
evolutionary processes across the cosmic epochs. In recent years major progress
has been made in constraining the chemical evolution of galaxies and inferring
key information relevant to our understanding of the main mechanisms involved
in galaxy evolution. In this review we provide an overview of these various
areas. After an overview of the methods used to constrain the chemical
enrichment in galaxies and their environment, we discuss the observed scaling
relations between metallicity and galaxy properties, the observed relative
chemical abundances, how the chemical elements are distributed within galaxies,
and how these properties evolve across the cosmic epochs. We discuss how the
various observational findings compare with the predictions from theoretical
models and numerical cosmological simulations. Finally, we briefly discuss the
open problems the prospects for progress in this field in the nearby future.
