Walter Carl Clemens, Jr. (born April 6, 1933) is an American political scientist best known for advancing complexity science as an approach to the study of international relations and comparative politics. He has been active in the analysis of complexity science, arms control and disarmament, and U.S. relations with communist and post-communist countries. Since 2008, he has been a regular contributor to Global Asia, the quarterly journal of the East Asia Foundation. He has authored numerous books, articles, and editorials, and is currently a Professor Emeritus at Boston University and an Associate at Harvard University's Davis Center for Russian and Eurasian Studies.