The Ge-Zr system is assessed by means of calculation of phase diagram (CALPHAD) approach, supplemented with decisive experiments and enthalpies of formation computed via Vienna ab initio simulation package (VASP) code. Nine Ge-Zr alloys were prepared by arc melting the pure elements. The annealed samples were analyzed by means of XRD, optical microscopy, and SEM/EDX. Five compounds are observed in the equilibrium condition. The enthalpies of formation for Zr5Ge3, Zr5Ge4, and ZrGe2 are computed via first-principles calculations. These enthalpies of formation are used as key "experimental data" in the CALPHAD approach in order to obtain the thermodynamic parameters with sound physical meaning. A consistent thermodynamic data set for the Ge-Zr system is finally obtained based on the present work and the literature data. Comparisons between the calculated and measured phase diagram and thermodynamic quantities show that the accurate experimental information is satisfactorily accounted for by the present thermodynamic description.