The spectral energy distribution of the light emitted from galaxies across the electromagnetic spectrum contains a myriad of details about the stellar, nebular and dust components of galaxies. In this thesis, we present a new approach to assess the relative merits of different types of observations to constrain galaxy physical parameters. To this goal, we build a comprehensive library of galaxy spectral energy distributions by combining the semi-analytic post-treatment of a large cosmological simulation with state-of-the-art models of the stellar and nebular emission and attenuation by dust. A main novelty of our approach is the ability to interpret simultaneously the stellar and nebular emission from galaxies, even at low spectral resolution. We first analyze the medium-resolution, rest-frame optical spectra of a sample of ~ 13,000 nearby star-forming galaxies extracted from the Sloan Digital Sky Survey. Then, we apply our approach to the analysis of combined photometric and spectroscopic observations of a sample of galaxies at redshifts between 1 and 3. Finally, we use our approach to simulate observations of primeval galaxies with the NIRSpec instrument onboard the future James Webb Space Telescope. The approach developed in this thesis can be used to extract valuable information from any kind of galaxy observation across the wavelength range covered by spectral evolution models as well as to plan for future galaxy observations.
