This　study　presents　the　thermodynamic　modeling　of　the　Ir-Mo　and　Ir-W　systems　by　means　of　the　CALPHAD　(CALculation　of　PHAse　Diagrams)　approach　supported　with　the　first-principles　calculations.　A　critical　evaluation　of　the　phase　equilibria　and　the　thermodynamic　property　data　in　literature　was　conducted　for　both　systems.　Due　to　the　lack　of　experimental　data,　the　first-principles　calculations　were　applied　to　obtain　the　enthalpies　of　the　solid　and　intermetallic　phases.　The　thermodynamic　parameters　were　assessed　using　the　PARROT　module　of　Thermo-Calc.　A　set　of　self-consistent　parameters　for　the　Ir-Mo　and　Ir-W　systems　was　obtained　after　the　optimization.　Satisfactory　agreement　between　the　calculated　results　and　the　experimental　data,　including　phase　equilibria　and　thermodynamic　properties　was　achieved.