In nonstandard analysis, the transfer principle is the technical form of the following intuitive idea: "Anything provable about a given superstructure by passing to a nonstandard enlargement of is also provable without doing so, and vice versa." It is a result of Łoś' theorem and the completeness theorem for first-order predicate logic

The transfer principle is stated as follows. Let be a superstructure, let be an enlargement of , let be any sentence in the language for , and let denote the -transform of . Then if and only if .