[Revised entry by Jeffrey Barrett on June 20, 2023. Changes to: Main text, Bibliography] Hugh Everett III proposed solving the quantum measurement problem by adopting pure wave mechanics, the theory one gets by dropping the collapse dynamics from the standard von Neumann formulation of quantum mechanics. Everett's relative state formulation consists in pure wave mechanics supplemented with a distinction between absolute and relative states, a model of situated observation, and a standard of typicality. His aim was to recapture the predictions of the standard collapse theory by showing that the relative records of a typical...