Since the last reviews 1 , 2 of experimentally determined spontaneous fission properties, more information has been obtained concerning half-life systematics, the kinetic energies and mass distributions of the fission fragments, and neutron and photon emission at scission or from the excited fragments. From the latter data, information about the excitation energies of the fragments has also been inferred. A recent review of heavy ions and nuclear fission by Oganessian and Lazarev 2a also includes much information on spontaneous fission. A review of light-particle emission accompanying spontaneous and induced fission is given by Wagemans elsewhere in this volume; recent theoretical developments are reviewed in Volume I.