This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymer ceramic materials, and a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105 degrees C temperature range. It was subjected to 40 charge-discharge cycles at current densities ranging from 0.05 to 0.25 mA/cm(2). The reversible charge/discharge voltage profiles of the Li-O-2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultrahigh energy density electrochemical power source. We believe that the Li-O-2 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3256129] All rights reserved.