The aim of the 2nd International Workshop on Neutrino Oscillations and their Origin was to put together the efforts from various fields necessary for understanding neutrino oscillations in detail, from both experimental and theoretical points of view. One of the main experimental issues was to understand the absolute flux of both the atmospheric and the solar neutrinos in order to obtain detailed parameter information on neutrino oscillations. This volume of proceedings contains many discussions on phenomenology and theories about neutrino mass and oscillations. The topics include: solar...