ABSTRACTWe report superconductivity in Cs3 C60 at 40K using ac susceptibility measurements under hydrostatic conditions up to 15 kbar. Cs3 C60 was prepared by reaction of C60 with Cs in liquid ammonia, followed by heating at 150°C. This route circumvents formation of the energetically more stable CSl C60 and Cs4 C60 phases. We have studied the synthesis and phase formation by measuring the symmetric Ag pentagonal pinch mode of C60 using Raman spectroscopy. Whereas Raman spectroscopy indicates homogeneous charge transfer of three electrons, x-ray diffraction indicates two phases other than the commonly observed fcc structure. This superconducting transition temperature is considerably higher than for known doped C60 compounds and intermetallic compounds.