The advancement of observational techniques over the years has led to the discovery of a large number of stars exhibiting complex spectral structures, thus necessitating the search for new techniques and methods to study radiative transfer in such stars with moving envelopes. This led to the introduction of the concept of "photon escape probability" and the wisdom of expressing the transfer equations in "comcoving frames" (CMF). Radiative transfer problems in spherically moving media form a branch of mathematical physics which uses mathematics of a very distinctive kind. This text records the basic mathematical methodologies, both analytical and numerical, developed for solving radiation transfer problems in spherically symmetric moving media, in the consideration of macroscopic velocity fields only. Part one contains the basic notions of radiation-matter interaction in participating media and constructs the relevant transfer equations to be solved in the subsequent chapters. Part two considers the basic mathematical methods for solving the transfer problems in extensive moving atmospheres when it is observed in the lab frame. Part three introduces the analytical and numerical methods for solving radiative transfer problems in spherically symmetric moving atmospheres when expressed in the comoving frame.