  We propose the liquid-scintillator detector LENA (Low Energy Neutrino
Astronomy) as a next-generation neutrino observatory on the scale of 50 kt. The
outstanding successes of the Borexino and KamLAND experiments demonstrate the
large potential of liquid-scintillator detectors in low-energy neutrino
physics. LENA's physics objectives comprise the observation of astrophysical
and terrestrial neutrino sources as well as the investigation of neutrino
oscillations. In the GeV energy range, the search for proton decay and
long-baseline neutrino oscillation experiments complement the low-energy
program. Based on the considerable expertise present in European and
international research groups, the technical design is sufficiently mature to
allow for an early start of detector realization.
