In this monograph a leading modern astrophysicist explores a problem basic to stellar dynamics: What is the relationship between loss of energy, mass, and radius of stars in the steady state?The monograph is divided into two distinct parts. In chapters i-iv, Chandrasekhar presents the ""classical"" background necessary to his argument: the laws of thermodynamics (from Caratheodory's rigorous axiomatic standpoint), adiabatic and polytropic laws, and the work of Ritter, Emden, Kelvin, and others who developed the applied mathematics of stellar structure. Chapters v-xii discuss modern results: the formal theory of radiation, the equations of radiative equilibrium, the luminosity formula, the theory of stellar envelopes, Gibbs statistical mechanics (the quantum mechanical version), white dwarfs, etc. The closing chapter outlines some general trends in current investigations of the problem.Appendixes cover physical and astronomical constants; the masses of light atoms; the masses, luminosities, and radii of the stars, derived hydrogen contents, central densities and central temperatures, and tables of white dwarf functions.""Extremely interesting. It reaches the highest level of scientific merit."" - Bulletin, American Mathematical Society.