Neutrino physics with the KamLAND detector

We present the initial design of a very large liquid scintillator detector to be installed in the underground cavity where Kamiokande was once sited. The experiment is optimized to detect low-energy anti-neutrinos and will pe rform unique measurements in the fields of neutrino physics, geophysics and astrophysics. KamLAND is conceived as a "scalable" detector that will be a ble to start in a very short time. This first stage detector will be able t o deliver results on a number of essential physics issues that only require present day technology. This first running period will also establish back grounds and detector requirements for a second ultra-low background running phase. One of the initial aims will be to perform a very long baseline osc illation experiment using several nuclear reactors. This can be considered the "ultimate" neutrino mass test using the oscillation technique. The obse rvation of neutrinos from the Earth, supernovae, atmosphere and nucleon dec ay will also be part of a very ambitious initial program, while in a later stage the observation of solar neutrinos will become the main focus.