Maraston (2005) presents evolutionary population synthesis models for a wide range of metallicities, ages, star formation histories, initial mass functions, and Horizontal Branch morphologies, including blue morphologies at high metallicity. The models compute spectral energy distributions, colours, stellar M/L ratios, bolometric corrections, and near-infrared spectral line indices. The energetics of post Main Sequence phases are evaluated using the fuel consumption theorem. The impact of stellar evolutionary tracks (with and without overshooting) on the models is assessed. The models show modest differences in synthetic broad-band colours, with Δ(V - K) ~ 0.08 mag and Δ(B - V) ~ 0.03 mag. These differences are smaller than scatter among other models in the literature. The models are calibrated with globular cluster data from the Milky Way for old ages and with Magellanic Clouds and NGC 7252 for young ages. The contribution of the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) phase is emphasized. The TP-AGB phase is crucial for modeling young stellar populations, as shown by comparisons with observed spectral energy distributions of Magellanic Clouds clusters. The combination of near-IR spectral indices C₂ and H₂O can determine the metallicity of ~1 Gyr stellar populations. The models are applied to high-z galaxies (z ~ 2.4–2.9) observed with the Spitzer Space Telescope, showing that TP-AGB stars are essential for reproducing their near-IR fluxes, suggesting formation redshifts around z ~ 3–6. The paper discusses the algorithm, ingredients, and applications of the models, emphasizing the importance of the TP-AGB phase in evolutionary population synthesis. The models are calibrated with various stellar evolutionary tracks and show differences in fuel consumption, temperatures, and surface gravities. The transformations to observables are based on theoretical and empirical models, with the BaSeL library used for synthetic stellar spectra. The empirical spectra for TP-AGB stars are based on observations of C- and O-type stars. The paper highlights the importance of the TP-AGB phase in modeling stellar populations and its impact on the derived properties of galaxies.Maraston (2005) presents evolutionary population synthesis models for a wide range of metallicities, ages, star formation histories, initial mass functions, and Horizontal Branch morphologies, including blue morphologies at high metallicity. The models compute spectral energy distributions, colours, stellar M/L ratios, bolometric corrections, and near-infrared spectral line indices. The energetics of post Main Sequence phases are evaluated using the fuel consumption theorem. The impact of stellar evolutionary tracks (with and without overshooting) on the models is assessed. The models show modest differences in synthetic broad-band colours, with Δ(V - K) ~ 0.08 mag and Δ(B - V) ~ 0.03 mag. These differences are smaller than scatter among other models in the literature. The models are calibrated with globular cluster data from the Milky Way for old ages and with Magellanic Clouds and NGC 7252 for young ages. The contribution of the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) phase is emphasized. The TP-AGB phase is crucial for modeling young stellar populations, as shown by comparisons with observed spectral energy distributions of Magellanic Clouds clusters. The combination of near-IR spectral indices C₂ and H₂O can determine the metallicity of ~1 Gyr stellar populations. The models are applied to high-z galaxies (z ~ 2.4–2.9) observed with the Spitzer Space Telescope, showing that TP-AGB stars are essential for reproducing their near-IR fluxes, suggesting formation redshifts around z ~ 3–6. The paper discusses the algorithm, ingredients, and applications of the models, emphasizing the importance of the TP-AGB phase in evolutionary population synthesis. The models are calibrated with various stellar evolutionary tracks and show differences in fuel consumption, temperatures, and surface gravities. The transformations to observables are based on theoretical and empirical models, with the BaSeL library used for synthetic stellar spectra. The empirical spectra for TP-AGB stars are based on observations of C- and O-type stars. The paper highlights the importance of the TP-AGB phase in modeling stellar populations and its impact on the derived properties of galaxies.