Neutrinos
  We can start with the question: why are neutrino properties especially interesting? Recall that in the minimal standard model there are no right handed neutrinos and furthermore lepton number is conserved so neutrinos can have neither Dirac nor Majorana masses. Furthermore, with zero masses, the mixing angles in the charged weak current are all zero. Any evidence for non-zero masses or mixing angles is evidence for physics beyond the standard model and hence potentially a powerful tool. Besides, the masses and mixing angles are fundamental parameters which will have to be explained by the eventual theory of fermion masses. 
S. Pakvasa (University of Hawaii at Manoa)