There is need to double the world protein supply before 1990, and this need is most acute in the developing countries, or LDC's. For a solution to the world's food problems, one must look not only to the more efficient use of all the known sources of food and protein, but the development of new nutritional sources along with an assessment of the technical and economic feasibility of doing so. Stressing that the development and use of the world's fishery resources form part of the problem of assessment, we note the following: (1) With respect to capture fisheries, the present yield is about 65 million metric tons, while the potential is for a harvest almost double that amount. Geographically this potential exists largely in the waters of, or adjacent to, the developing countries. (2) With respect to aquaculture, the present yield is 5 to 10 percent of the yield of the capture fisheries, but it has a greater potential for increase -- in the order of fivefold growth or, perhaps, substantially more. With supporting research and planning, the growth of aquaculture is often particularly well suited to developing countries. (3) Much of the development of capture fisheries and aquaculture in the LDC's can be handled best as labor intensive, relatively low-capital undertakings. (4) To the extent that these developing countries also move into more offshore ventures requiring more capital, they may run into competition, even conflict, with more developed nations that are continually expanding into new resource areas distant from their shores. (5) Economically, the prospects for developing the fisheries are favorable in that (where subject to comparison) the cost per pound of producing fish protein, both in the capture fisheries and aquaculture, is often less than the cost for other protein sources of equivalent quality.