This chapter argues that the electromagnetic interaction has everything to do with the phase of wavefunctions, and hence presumably of their quantum field generalizations: fields which are real must be electromagnetically neutral. Central to the satisfactory physical interpretation of the Dirac field will be the requirement that it must be quantized with anticommutation relations – the famous ‘spin-statistics’ connection. In general ‘particle’ and ‘antiparticle’ are distinguished by having opposite values of one or more conserved additive quantum numbers. Similar difficulties would have occurred in the complex scalar field case if we had assumed anticommutation relations for the boson operators, and the ‘causality’ discussion at the end of the preceding section would have worked either. It is in this way that quantum field theory enforces the connection between spin and statistics.