During his career, Caldwell served on the faculties of the University of Chicago, Northwestern University, the University of Oklahoma, Syracuse University, and the University of California at Berkeley, and had shorter appointments at some 80 other collegiate institutions both within the U.S. and overseas. At various times, Caldwell served as advisor or consultant to the U.S. Senate, UNESCO, the United Nations, the Departments of Commerce, Energy, Defense, and Interior, and the National Institutes of Health. Although not a natural scientist, as part of his work towards establishing interdisciplinary study in universities and achieving a greater merging of the two worlds of science and public policy, he became deeply involved in national and international environmental affairs and worked closely with several important scientific bodies serving, among many appointments, on the Sea Grant Program of the National Oceanic and Atmospheric Administration (NOAA), the first Environmental Advisory Board of the United States Army Corps of Engineers, the Pacific Science Congress, the President’s National Commission on Materials Policy, the Science Advisory Board for the Great Lakes of the International Joint Commission, as chair of the first Commission on Environmental Policy, Law and Administration for the International Union for the Conservation of Nature and Natural Resources (IUCN), and as advisor to the UNESCO Man and the Biosphere Program (MAB), and the UNESCO working program for the environmental education and training of engineers.