Bruzual and Charlot present a new model for computing the spectral evolution of stellar populations at ages between 1×10⁵ and 2×10¹⁰ years, with a resolution of 3 Å across the wavelength range 3200–9500 Å. The model incorporates a new library of observed stellar spectra and accounts for recent advances in stellar evolution theory, including thermally pulsing stars on the asymptotic giant branch. The model reproduces observed optical and near-infrared colour–magnitude diagrams of Galactic star clusters and galaxy spectra from the Sloan Digital Sky Survey. It allows for accurate studies of absorption-line strengths in galaxies and can constrain physical parameters such as star formation history, metallicity, and dust content. The model is particularly useful for interpreting modern spectroscopic surveys in terms of galaxy constraints. The model uses a combination of stellar evolution prescriptions and spectral libraries to simulate the spectral evolution of stellar populations across a wide range of metallicities and ages. It includes detailed evolutionary tracks for stars, including TP-AGB and post-AGB phases, and incorporates observational data to improve accuracy. The model is validated against observations of star clusters and galaxies, demonstrating its effectiveness in reproducing photometric evolution and spectral properties. The model also includes a detailed treatment of carbon stars and stars in the superwind phase, using observational data and theoretical models to ensure accuracy. The model is based on the isochrone synthesis technique, which allows for the computation of spectral evolution based on star formation history and metallicity. The model is calibrated using a combination of theoretical and observational data, ensuring that it accurately represents the spectral evolution of stellar populations across a wide range of conditions.Bruzual and Charlot present a new model for computing the spectral evolution of stellar populations at ages between 1×10⁵ and 2×10¹⁰ years, with a resolution of 3 Å across the wavelength range 3200–9500 Å. The model incorporates a new library of observed stellar spectra and accounts for recent advances in stellar evolution theory, including thermally pulsing stars on the asymptotic giant branch. The model reproduces observed optical and near-infrared colour–magnitude diagrams of Galactic star clusters and galaxy spectra from the Sloan Digital Sky Survey. It allows for accurate studies of absorption-line strengths in galaxies and can constrain physical parameters such as star formation history, metallicity, and dust content. The model is particularly useful for interpreting modern spectroscopic surveys in terms of galaxy constraints. The model uses a combination of stellar evolution prescriptions and spectral libraries to simulate the spectral evolution of stellar populations across a wide range of metallicities and ages. It includes detailed evolutionary tracks for stars, including TP-AGB and post-AGB phases, and incorporates observational data to improve accuracy. The model is validated against observations of star clusters and galaxies, demonstrating its effectiveness in reproducing photometric evolution and spectral properties. The model also includes a detailed treatment of carbon stars and stars in the superwind phase, using observational data and theoretical models to ensure accuracy. The model is based on the isochrone synthesis technique, which allows for the computation of spectral evolution based on star formation history and metallicity. The model is calibrated using a combination of theoretical and observational data, ensuring that it accurately represents the spectral evolution of stellar populations across a wide range of conditions.