This present book is concerned with analytical approaches to statement and solution of problems of non-equilibrium evaporation and condensation. From analytical solutions, one is capable to understand and represent in a transparent form the principal laws, especially in the study of a new phenomenon or a process. This is why analytical methods are always employed on the first stage of mathematical modeling. Analytical solutions are also used as test models for validation of results numerical solutions. Non-equilibrium evaporation and condensation processes play an important role in a number of fundamental and applied problems: laser methods for processing of materials, depressurization of the protection cover of nuclear propulsion units, solar radiation on a comet surface, explosive boiling of superheated liquid, thermodynamic principles of superfluid helium. Analytical relations provide an adequate description of the essence of a physical phenomenon. .