The thermodynamic properties of zirconium nitride are presented, including the phase diagram of the Zr—N system, homogeneity region, temperature and composition corresponding to congruent melting of ZrN_x, enthalpy of formation, as well as electronic structure and chemical bond in zirconium nitride. An equation is given approximating the temperature dependence of the heat capacity of crystalline ZrN in the temperature range of 298.15—3970 K. Temperature dependences of specific heat and electrical resistance of liquid zirconium nitride of the composition 0.9ZrN+0.1ZrO₂ (up to 4500 K) measured by heating with a microsecond current pulse are presented. The main practical significance of these results is that ZrN serves as an inert matrix for mixed nitride fuel (U, Zr)N and (Pu, Zr)N for fast neutron reactors.