  We consider main ingredients which determine neutrino transformations in
media. Strong transformations relevant for the astrophysics can be due to large
depth oscillations, resonance conversion, parametric resonance effect,
interplay of oscillations and inelastic collisions. Properties of transitions
are discussed using the graphic representation. The applications of the
transitions to supernova neutrinos are described. The supernova neutrinos can
probe whole neutrino mass spectrum. Their studies will help to identify the
pattern of neutrino mass and mixing.
