This chapter develops the measurement interpretation of quantum mechanics. This is an austere systematized version of the orthodox Copenhagen interpretation. Dirac used an analysis of the distinctive features of quantum measurements as a basis for developing the mathematical formalism of quantum mechanics. Schwinger put this on a more systematic basis and extended the formalism to include quantum electrodynamics and basic quantum field theory. This measurement formulation does not accommodate further advances in quantum field theory or quantum cosmology, where there is no outside observer.