Types and peculiarities of liquid membrane extraction are surveyed. The properties of bulk, supported, and emulsion liquid membranes are given. The basic principles of liquid membrane extraction, the types of carriers, and the stability of systems in the course of processes are considered. The use of liquid membranes for the separation of gas mixtures is demonstrated. The advantage of membrane extraction is the possibility of achieving high degrees of extraction and concentration in a single stage. At the same time, the organization of a membrane extraction process is more complicated than that of traditional processes.