Galaxies emit across the electromagnetic spectrum. Excluding those galaxies dominated by an accreting supermassive black hole at their nucleus (AGN), the ultraviolet to infrared spectra of all galaxies arises from stellar light, either directly or reprocessed by the gas and dust of the surrounding interstellar medium (ISM). Thus the UV-to-IR spectral energy distribution or SED contains a large amount of information about the stars of a galaxy, such as the stellar mass to light ratio, and the surrounding ISM, such as the total dust mass. However, to extract such information, models are necessary in order to connect physical properties of the galaxy with the observed SED. In this section we discuss such models, beginning with the stellar spectrophotometric models, moving on to the transfer of the radiation of these stars in a galaxy through the ISM, and finally how to connect these with the larger picture of galaxy formation and evolution. We use the following abbreviations for designing wavelength ranges, though the exact boundaries between wavelength regimes are not sharp: ultraviolet (UV) for λ<3500 Å, optical for 3500<λ<8000 Å, near infrared (NIR) 0.8<λ<3 μm, mid-infrared (MIR) 3<λ<25 μm, far-infrared (FIR) 25<λ<250 μm, sub-mm 0.25<λ<1 mm, and radio λ>1 mm.