This article reviews our present knowledge of neutrino interactions with nucleons. It then discusses the interactions with nuclei, the target material of all presently running and planned long-baseline experiments. Particular emphasis is placed on descriptions of semi-inclusive reactions and full descriptions of the final state; the latter are needed to reconstruct the incoming neutrino energy from final state observations. Monte-Carlo generator and more advanced transport theoretical approaches are then discussed in connection with experimental results on various reaction mechanisms. Finally the effects of uncertainties in the reconstruction of the incoming neutrino energy on oscillation parameters are described. It is argued that the precision era of neutrino physics also needs precision era generators.