Nuel D. Belnap Jr. (//; born 1930) is an American logician and philosopher who has made contributions to the philosophy of logic, temporal logic, and structural proof theory. He taught at the University of Pittsburgh since 1963 until his retirement in 2011; before that he was at Yale University. His best-known work is his collaboration with Alan Ross Anderson on relevance logic. He has also published books on the logic of questions and answers, with Thomas Steel, and the logic of agency, with Michael Perloff and Ming Xu. He has contributed to the foundations of two very distinct theories of truth: he was a co-author of The Prosentential Theory of Truth with Dorothy Grover and Joseph Camp, and of The Revision Theory of Truth with Anil Gupta. He is also co-author with Ming Xu and Michel Perloff of Facing the Future. He was elected a Fellow of the American Academy of Arts and Sciences in 2008.