This chapter introduces the categoricity problem for a representationalist metasemantics of quantum mechanics (QM). Some intended limitations of the descriptive completeness of scientific theories are first presented, motivated by the view advocated by Hertz and Weyl, that some things are beyond what a complete theory ought to tell us about its domains of application. After specifying a proper notion of categoricity for standard QM, and responding to some possible objections, an intuitive reading of the Stone-von Neumann theorem as a categoricity result is critically discussed. Drawing on this, a new reconstruction of Einstein’s incompleteness argument is proposed.