M. Sorel, IFIC (Valencia U. & CSIC)
The K2K experiment in Japan has been the first long-baseline accelerator-based experiment to confirm atmospheric neutrino oscillations. The experiment took data between 1999 and 2004, and final neutrino oscillation results on the measurement of muon neutrino disappearance and on the search for electron neutrino appearance have both been published in 2006. The K2K oscillation results, together with their physics implications, are reviewed. Finally, the lessons learned from this pioneering long-baseline neutrino experiment are discussed, with an eye toward next-generation experiments of this type, such as T2K.