NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the board responsible for the report were chosen for their special competencies and with regard for appropriate balance.

This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

Support for this project was provided by the Ford Foundation under Agreement No. 910–1413, the Tinker Foundation, the U.S. Environmental Protection Agency under Agreement No. CX-820728–01–0, the Mexico National Science and Technology Council (CONACYT), the Mexico Ministry of Health, the United Nations Development Program, the National Research Council Fund, the Rockefeller Foundation, and the MacArthur Foundation.

About the Cover: Paisaje by Emilio Rosenblueth, oil on canvas, 1938; collection of the Rosenblueth family. Use of this painting is in memory of Emilio Rosenblueth, Jr. (1926–1994), son of the artist, who did much for the advancement of science in Mexico and was so instrumental in building bridges to the scientific community in the United States. Dr. Rosenblueth, Jr. was director of the Institute of Engineering of the National University of Mexico (UNAM), the dean of science for the university, president of the Academy of Science (AIC), vice-minister of the Ministry of Education, and foreign associate member of NAS and NAE. Special thanks to Sra. Alicia Laguette de Rosenblueth, wife and companion of Emilio, and his family for permission to reprint.