Critical review of the Fe-Y binary system has been performed and available experimental and calculated data have been collected. Thermodynamic parameters were optimized using the CALPHAD method. New experimental results of Gibbs energy and Ab-initio calculations of enthalpy of formation of intermetallic compounds have been taken into account. A self-consistent thermodynamic description of the Fe-Y system has been obtained. Problems of thermodynamic modelling in this system have been discussed. The results calculated using thermodynamic descriptions derived in the present work are compared with ones previously published using general “χ2”-criterion. This criterion allows taking into account the number independent optimized parameters used in the optimization. The calculated agreement criterion has shown that thermodynamic description of the present work describes experimental data better than earlier published ones.