UNO (Underground Neutrino Observatory) is intended as a multi-purpose detector, potentially useful for purposes which may not have been considered at the time of its construction. UNO accomodates a comprehensive physics program, encompassing nucleon decay and lepton flavor physics, including the possibility of observing CP violation, grand unification scale physics, and detailed observations of supernova explosions. The conceptual design of UNO is described, along with specifics of how UNO would fit into an existing commercial mine site in the western USA, which has been used as a strawman site for planning and proposal development.

Comment: Talk given at XI International Workshop on ``Neutrino Telescopes'', Feb 22-25, 2005, Venice, Italy; 19 pages, 7 figures