Supernova neutrino observations: What can we learn?

Twenty years after SN 1987A, the vast international programme of experimental neutrino physics and neutrino astronomy suggests that large detectors will operate for a long time. It is realistic that a high-statistics neutrino signal from a galactic SN will be observed. I review some of the generic lessons from such an observation where neutrinos largely play the role of astrophysical messengers. In principle, the signal also holds valuable information about neutrino mixing parameters. I explain some recent developments about the crucial importance of collective neutrino oscillations in the SN environment.