  Future neutrino-oscillation experiments are expected to bring definite
answers to the questions of neutrino-mass hierarchy and violation of
charge-parity symmetry in the lepton sector. To realize this ambitious program
it is necessary to ensure a significant reduction of uncertainties,
particularly those related to neutrino-energy reconstruction. In this paper, we
discuss different sources of systematic uncertainties, paying special attention
to those arising from nuclear effects and detector response. By analyzing
nuclear effects we show the importance of developing accurate theoretical
models, capable to provide quantitative description of neutrino cross sections,
together with the relevance of their implementation in Monte Carlo generators
and extensive testing against lepton-scattering data. We also point out the
fundamental role of efforts aiming to determine detector responses in test-beam
exposures.
