The number of neutrinos detected from the sun is only a fraction of what should be detected if our understanding of the nuclear reactions in the sun is correct. A proposed solution to this problem is that neutrinos change from one flavor to another on their travel from the sun to Earth. This phenomenon is called neutrino oscillation. It can only occur if the neutrinos have a small mass. Most experiments that support neutrino oscillation measure the lack of neutrinos of one flavor that they interpret as an oscillation into an undetected flavor. Recently an experiment has detected tau neutrinos in a muon-neutrino beam from an accelerator at CERN and a detector, 732 kilometers away, in the Gran Sasso tunnel in Italy. This flavor change supports neutrino oscillation.