Presently ongoing or planned neutrino long baseline experiments all use nuclear targets. Any extraction of neutrino properties from observables in such experiments thus has to deal with the in-medium production and the final state interactions of outgoing particles. Traditionally, this has been done with neutrino event generators. In this talk I will show that the widely used neutrino generators have not yet reached the degree of sophistication of the experimental equipment for neutrino experiments. I will disuss the essential nuclear physics input for neutrino generators: QE, many-body interactions, pion production through resonances and DIS. I will then illustrate how all of these processes affect the event characterization, energy reconstruction and the extraction of neutrino oscillation parameters, using results from the nuclear physics based transport code GiBUU.