The Electron nuclear dynamics (END) theory is a time-dependent, nonadiabatic approach to molecular processes. It has been implemented in the ENDyne code at the level of approximation that treats the nuclei as classical particles and represents the electrons with a single complex spin unrestricted determinant. This level of theory has been successfully applied to a wide range of ion-atom and ion-molecule reactive collisions. In this paper the extensions of the END theory are outlined in some detail through a hierarchy of approximations to the level of full quantum mechanical treatment of all participating particles.