Super-Kamiokande is the third in a succession of large underground water Cherenkov detectors. Previously, there was the IMB (Irvine-Michigan-Brookhaven) and Kamiokande (Kamioka-Nucleon-Decay-Experiment) experiments. Their primary purpose was initially to search for Nucleon Decay, however as the products of these decays continually failed to appear another, possibly more interesting, problem developed. There was something wrong with the measured ratio of muon neutrinos to electron neutrinos. The neutrinos in question come from interactions between the primary cosmic ray flux with Earth's atmosphere. This has since been known as the Atmospheric Neutrino Problem. However, this is by no means the worlds first neutrino problem. Back in the late 1960's were the first reports from R. Davis's solar neutrino detector in Homestake. It was here that the first reports of measurements of a solar neutrino flux which was significantly lower than theoretical predictions. Work on refining measurements of Solar Neutrinos continues today at Super-Kamiokande.
For a general overview of the neutrino physics studied by the Super-Kamiokande group and other neutrino physicists please see http://superk.physics.sunysb.edu/~alpinist/pub/apctp_main_9.ps.