We consider the state of the art of the research into the IR spectroscopy of high-temperature (T < 3000 K) water vapor. Physical models for description (within the framework of direct line-by-line calculations) of absorption coefficient and emissivity of high-temperature water vapor are discussed. A particular attention is paid to the development of the software for compilation of spectroscopic databases of water vapor spectral line parameters based on HOTGAS-H2O information generation system. Using standard assumptions (radiation diffusion and local thermodynamic equilibrium within one layer), the water vapor emissivity was calculated for various concentrations and temperatures from 300 to 3000 K. The stratified medium was simulated by plane-parallel layers of different thickness. The approximations of absorption coefficients considerably simplifying the calculations were proposed based on direct methods. The values of nonselective component of the water vapor absorption coefficient in the range from 8 to 12 mm and temperatures from 1500 to 3000 K are presented for the first time.