2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/123245I present a short description of the STELIB, HNGSL, IndoUS, MILES, ELODIE, UVES-POP, and IRTF libraries of empirical stellar spectra and show some applications of their use in population synthesis models. When new calculations of the TP-AGB evolutionary phase for stars of different mass and metallicity are included in population synthesis models, the stellar mass in galaxies at z from 1 to 3 determined from spectro-photometric data can be up to 50% lower than the mass determined from the BC03 models. The ages inferred for these populations are considerably lower than the BC03 estimates.8 pages, 5 figures, in Proceedings of the Meeting "From Stars to Galaxies: Building the Pieces to Build Up the Universe", eds. A. Vallenari, R. Tantalo, L. Portinari, and A. Moretti, ASP Conf. Ser. (in press)Astrophysicstext