Is the Copenhagen interpretation really a subjective one? What is the special role that observations play in quantum theory? Is there really something peculiar about the projection postulate? Why does the Copenhagenist treat probabilities as properties of individual systems? Is there a measurement problem, and if so, can itin principle be solved within the framework of quantum theory? We offer aconceptual treatment of the Copenhagen interpretation of quantum mechanics in which these questions are answered and contrast it with another interpretation (...) which we call Popperism. The interpretations differ in their choice of a state description, from which it follows that they will offer a different account of the relation of measurements to states and different ways of describing quantum theory. But the two descriptions are equally consistent and physically completely equivalent. (shrink)