The flavour problem in the neutrino sector and in general in particle
physics is one of the most fundamental issue that still have to be
solved. Discrete non-Abelian discrete symmetries can play a crucial
role as family symmetries of the Lagrangian of particle interactions.
Specifically they could be symmetries of the PMNS mixing matrix. As
example I will review in this talk the role of T', a group with
complex Clebsch-Gordan coefficients, combined with the SM gauge
group.
