Two leading neutrino physicists have won the 2015 Nobel Prize in Physics for their work on neutrino oscillation.
Neutrino physics remains a work in progress.
The three main parameters governing neutrino oscillation (mixing angels theta12, theta13 and theta23) and the relative masses of the three neutrino mass eigenstates (delta m12 and delta m23) has been established (although not always with the precision desired).
But, there are important outstanding questions regarding the nature of neutrino mass (Dirac or Majorana, through the Higgs mechanism or otherwise such as a see-saw mechanism), the absolute values of the neutrino masses, the CP violating phase of neutrino oscillation (if any), and the possibility that more particles (e.g. "sterile" right handed neutrinos) or more complex models than the PMNS matrix may be necessary to describe neutrino oscillation completely.
Backreaction examines the work of the prize winners in more detail.