Abstract
This article is the combination of a review and some new results of kinetic theoretical studies on the half-space problem of evaporation and condensation. A semi-infinite expanse of a gas uniform at infinity and bounded by its plane condensed phase is considered. Steady flow, evaporating from or condensing onto the condensed phase depending on the parameters of the condensed phase and the infinity, and the relation among the parameters that allows a steady solution are studied. Special attention is paid to the difference of the character of the relation, depending on evaporation, subsonic condensation, or supersonic condensation, and analytic structure of the transition of the relation and solution from evaporation to subsonic condensation or from subsonic condensation to supersonic one.