  This article outlines a method to interpret the extragalactic background
light in terms of the large-scale, average properties of galaxies, including
the comoving densities of stars and interstellar gas, metals, and dust. These
quantities are related by a series of coupled conservation-type equations
analogous to the equations of galactic chemical evolution. This approach
enables us to combine observations of the emission and absorption in galaxies
and thus to relate their average stellar and interstellar contents.
Applications of the method include predictions of the global history of star
formation from absorption-line observations and corrections to the cosmic UV
emissivity for absorption by dust.
