Aspects of the Symmetry Approach to Neutrino Masses and Mixing

In the present thesis we investigate distinct facets of the symmetry approach to neutrino masses and neutrino mixing. Regarding the symmetry approach to neutrino masses, we focus on lepton number violation, namely its relation to Froggatt-Nielsen symmetry in a low-scale seesaw model and its potential observability in future neutrinoless double beta decay experiments. As for the symmetry approach to neutrino mixing, we consider the effects of non-Abelian discrete flavour symmetries in the lepton sector, which may be consistently combined with CP symmetry. We further discuss, in a bottom-up approach, the implications of a broken modular symmetry for neutrino masses and mixing.