  High-precision measurements in neutrino oscillation experiments require a
very accurate description of the lepton-nucleus scattering process. Several
cross-section calculations are available, but important discrepancies are still
present between different model predictions. For the quasi-elastic channel,
dominated by one particle-one hole excitations, an overview over several
nuclear models - specifically Relativistic Fermi Gas, SuperScaling Approach,
Spectral Function, Hartree-Fock and Random Phase Approximation - is presented
and compared with data for electron-nucleus scattering, a very important
process for testing theoretical models validity, highlighting the specific
features of each approach. Furthermore an ongoing microscopic calculation of
the two particle-two hole excitations contribution to the electromagnetic
response is presented, and some preliminary results are shown.
