AbstractA discussion of the quantum mechanics of molecules with the emphasis on quantum mechanical principles is presented in the expectation that a better understanding of the assumptions tacitly embodied in conventional quantum chemistry will follow. The discussion centres mainly on the position of the chemical structure hypothesis in a quantum mechanical theory based on quantum states. Various different kinds of molecular states are identified according to characteristic properties of their wavefunctions, ranging from the completely delocalized (fully symmetrized) eigenstates to the “molecular structure states” of rigid molecules. I suggest that the adiabatic separation of electrons and nuclei can be avoided by working with the generator coordinate method (GCM) which promises to be a powerful non‐adiabatic formalism for molecular quantum t