The theory of infinite-dimensional Lie (super)algebras differs markedly from the theory of finite-dimensional Lie (super)algebras in that the latter possesses powerful classification theorems, which usually allow one to "recognize" any finite- dimensional Lie (super)algebra (over the field of complex or real numbers), i.e., find it in some list. There are classification theorems in the theory of infinite-dimensional Lie (super)algebras as well, but they are encumbered by strong restrictions of a technical character. These theorems are useful mainly because they yield a considerable supply of interesting examples.