In recent years we have obtained strong evidence of neutrino oscillations, implying that neutrino are massive particle and that they mix. One of the fundamental questions for the future concerns the absolute values of neutrino masses. Their measurement requires to fix the absolute mass scale and the type of hierarchy.
After briefly illustrating how to measure the absolute mass scale in tritium beta decay experiments and by cosmological observations, I will discuss how to determine the type of hierarchy by using matter effects in long base line experiments. I will address the problem of degeneracies. I will focus in particular on NOvA and a possible addition of a second detector (Super-NOvA) at a shorter baseline which allows to resolve completely the degeneracies and to determine the type of hierarchy for sufficiently large values of theta13.

CERN and IPPP, Durham