ALL but the most minute amount of energy used to drive our transportation system, heat and light our homes, power our industry, and, indeed, supply the energy which we obtain from the food we consume, comes from the sun by way of Furthermore, all of this energy, whether it be fuel or food, comes from the nonliving to the living world across a single bridge known as the chlorophylls-the pigments of Controlled involves the bringing of sunlight energy across this chlorophyll bridge at a regulated rate and with a higher efficiency than normally occurs in nature. Applications of the process are already in use and its potential for solving many of mankind's fundamental problems both old and new is exciting widespread recognition. Therefore, the time is appropriate for a review of the process itself and a discussion of its use in the solution of a few of the more interesting and significant problems facing civilization. As used in this paper, the term photosynthesis refers to those processes in which photosynthetic organisms are produced continuously under partially or completely controlled environmental conditions. Two processes developed during the last decade can be classified as photosynthesis. The first is the continuous production of grasses on irrigated, continually grazed or harvested pasture land, according to the procedure described by Pirie.1 The second is the continuous culture and harvest of microscopic algae. Although continuous grass production has an important potential in present food production, the scope of its future application does not appear to be as broad as that of continuous cultures of algae, with which this paper is primarily concerned. A number of processes for culturing algae under controlled conditions has been devised. In these processes, algae are grown in shallow ponds designed to permit a maximum exposure of the surface to sunlight, in which nutrients are supplied continuously. Provision is made for the mixing required to prevent sedimentation of the algal solids. Culture is withdrawn continuously for separation of the algal cells. In one process originally studied in the United States,2 and then more extensively in Japan,3 algae were grown