We review the state of the art of the derivation of star formation histories from color-magnitude diagrams reaching the oldest main sequence turnoffs. From the observational point of view, high quality CMDs are being obtained for galaxies over virtually the whole Local Group. However, the retrieval of star formation histories from these data using the synthetic color magnitude diagram technique heavily relies on stellar evolution model predictions. We discuss the main systematic differences that are found among the stellar evolution libraries most heavily used for this purpose, and the effect that these differences have on the resulting star formation histories.