In Part III, we mainly consider the radiation hydrodynamics under the nonrelativistic regime. However, the radiation field of photons is essentially relativistic, and the radiation hydrodynamical technique becomes more and more important in various relativistic astrophysical phenomena. Thus, in the last four chapters of Part III, we consider the relativistic radiation hydrodynamics. In this chapter, corresponding to Chap. 22 for the nonrelativistic case, we first derive the basic equations for relativistic radiative transfer within the framework of special relativity in somewhat details. That is, we give the metric and quantities of the radiation fields, derive the radiative transfer equation and its formal solutions, obtain moment equations under special relativity, and discuss a closure relation in the relativistic regime. In addition, we shortly show several topics on the radiative transfer in the relativistic regime.