Pressure studies of phospholipid bilayer membranes are reviewed. The effect of pressure on the phase transition temperatures of dipalmitoylphosphatidylcholine bilayer membranes were determined by the various physical techniques including dilatometry, ESR, X-ray diffraction, fluorescence, Raman spectroscopy, neutron diffraction, light transmission, and NMR. In addition to the liquid crystal, ripple gel and lamellar gel phases, a new pressureinduced, interdigitated gel phase is presented.