Ever since Harrison, Perkins and Scott suggested that the neutrino
mixing data could be approximated by the tri-bimaximal mixing matrix,
there have been many proposals to explain its structure in terms of a
discrete family symmetry. In this talk we discuss two classes of
models - direct and indirect - which realise the effective neutrino
flavour symmetry in different ways. We illustrate both possibilities
in explicit models based on A4, S4 and PSL(2,7).
