Along with several other symposia of the Centennial Meeting of the American Association for the Advancement of Science, the symposium on the Sources of Energy was under the growing realization of the truths so aptly demonstrated by J. Osborne, W. Vogt, Stuart Chase and the conservationists: that humanity is on an unrepeatable spending spree, that we are using up mineral and energy resources on an unprecedented scale, and that these will run out in the foreseeable future. Because this symposium dealt with a rather well defined and clearly delimited facet of the whole problem, it could be attempted, with some prospect of success, to point to ways and means by which the apparently unescapable debacle can be avoided, at least as far as the exhaustion of energy sources is concerned. By making more direct use of the source of all terrestrial energy, the solar radiation, and by exploiting directly the source of solar radiation, the nuclear fuels, one can hope to provide the energy necessary for maintaining our standards of life into the indefinite future.