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 talk, I 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. We then rely on our sophisticated and physically motivated
models to derive predictions on the star formation histories of blue galaxies
at redshift z<1.4. We also 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.