A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the ternary Al2O3–B2O3–SiO2 system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model and the Gibbs energy of the mullite solid solution is modeled using the Compound Energy Formalism. A set of optimized internally consistent thermodynamic functions for all the phases is presented. With the thermodynamic dataset, all available and reliable thermodynamic and phase equilibrium data can be reproduced within experimental error limits from 25 °C to above the liquidus temperatures. In addition, the reasonable predictions obtained for phase relations in the experimentally unexplored composition ranges suggest that the thermodynamic database can be used along with appropriate Gibbs energy minimization routines to calculate thermodynamic properties, phase equilibria, and phase diagrams of interest.