The Mystery of Neutrino Mixing

In the last years we have learnt a lot about neutrino physics. A long list of models have been formulated to understand neutrino masses and mixings. Along the way, with the continuous improvement of the data, most of the models have been discarded by experiment. At present, the surviving models still span a wide range of possibilities, going from a maximum of symmetry, described by discrete non-abelian flavour groups, to the opposite extreme of anarchy. In particular, discrete flavour groups have been studied in connection with special patterns of neutrino mixing suggested by the data, like Tri-Bimaximal mixing (groups $A_4$, $S_4$...) or Bi-Maximal mixing (group $S_4$.... ) etc. We briefly summarize a number of models based on various patterns and symmetries and compare them with the experimental data.