MEIS is based on the interaction of a primary monoenergetic ion beam (typically 100 keV H+ or He+) with target nuclei. The energy and angle of the back-scattered particles are simultaneously analyzed with a toroidal electrostatic analyzer combined with a bi-dimensional position sensitive detector. Both parameters are related to the mass and in-depth position of the target atoms for the former, as well as to the surface structure for the latter. Moreover, the scattering yield can be quantitatively interpreted. MEIS is thus able to provide quantitative compositional and structural (defects and strain) information. In the MEIS energy range (50-400 keV) and thanks to the experimental setup, sub-nm depth resolution can be achieved in the near surface region, with picometer accuracy in measuring atomic displacements.