This is the report of the third Washington Colloquium on Science and Society. It contains the papers presented by the eight main speakers and the rebuttal and discussion which followed. The theme of the colloquium was "Changing Man in a Changing Environment," and the papers presented aspects of this theme as seen by different specialists in particular areas of study and knowledge. These included history of science, development of backward areas, legislative implications, communications, and the philosophy of science. Scientific problems of international development divide into those which affect the rich, namely the avoidance of nuclear war, computers, and the growth of cities, and those which affect the poor summarized under the provision of sufficient food. Changes in natural balances and the changes in man's social environment produced by scientific discoveries are discussed. (GR)