The constitutional and thermochemical information of the Co-Zr system is modelled using the Calphad method to obtain a reliable thermodynamic description of the system. Appropriate sublattice models are chosen to describe the Gibbs energy of all stable phases of the system. The Gibbs energies of the disordered BCCA2 and the ordered Co-Zr (BCCB2) are coupled using the orderdisorder model within the framework of sublattice formalism. Results from ab initio calculations are used to aid the optimization of Gibbs energy descriptions of Co-Zr3, Co-Zr2, and BCCB2 phases. Calculated phase diagram and thermochemical data are compared with the experimental data. © 2010 Elsevier Ltd. All rights reserved.