Joseph Yehuda Halpern (May 29, 1953 – February 13, 2026), born in Israel and who died in Ithaca, New York, was a computer scientist, engineer, artificial intelligence researcher, and university professor described variously as Israeli-American, American, or Canadian.^[1,4] He was a professor of computer science at Cornell University and associated with the Association for Computing Machinery.^[1]

Halpern completed his undergraduate studies at the University of Toronto with a bachelor's degree in 1975, after which he spent two years in Ghana teaching mathematics at a school as part of Canadian University Services Overseas (CUSO).^[5,6] He pursued graduate studies at Harvard University, earning a master's degree in 1979 and a doctorate in 1981 under Albert R. Meyer and Gerald Sacks with the dissertation 'Axiomatic definition of programming languages and logic of programs'.^[5,6] As a postdoctoral researcher, he worked simultaneously at Harvard University and the Massachusetts Institute of Technology (MIT). Starting in 1982, he conducted research at IBM until 1996, serving as manager of the mathematics group at the IBM Almaden Research Center from 1987 to 1989. During that period, he held visiting and consulting professorships at Stanford University, and in 1990 in Toronto. From 1996, he served as a professor at Cornell University, where he was co-director of the Cognitive Studies Program from 1996 to 2001 and chaired the computer science department beginning in 2010. He also served as a visiting professor on multiple occasions at the Hebrew University in Jerusalem, and in 2001–2002 at CWI in Amsterdam. Throughout his academic career, he was notably associated with collaborators and students including Nir Friedman, Daphne Koller, and Yoram Moses.

Most of his research focused on reasoning about knowledge and uncertainty, particularly in distributed systems, game theory, and artificial intelligence. He additionally worked on modal logic, decision theory, distributed computing and fault tolerance in distributed computing, program verification, causality, and the semantics of programming languages. In 1997, Halpern was awarded the Gödel Prize jointly with Yoram Moses for the formal definition of the concept of knowledge in distributed systems, and in 2009 both received the Dijkstra Prize.^[7] In 2008, he received the ACM-AAAI Allen Newell Award; he was also awarded a Senior Fellowship at the Zukunftskolleg of the University of Konstanz in 2011 and 2012, and was elected to the American Academy of Arts and Sciences in 2015 and the National Academy of Engineering in 2019.^[8]

Joseph Halpern was born on May 29, 1953 in Israel. He graduated in 1975 from the University of Toronto with a B.S. in mathematics and went on to earn a Ph.D. in mathematics from Harvard University in 1981 under the supervision of Albert R. Meyer and Gerald Sacks.

Regarding his books, English Wikipedia states that he has written three books—Actual Causality, Reasoning about Uncertainty, and Reasoning About Knowledge—whereas Spanish Wikipedia states that he has written two books, Reasoning about Uncertainty and Reasoning About Knowledge. He won the 1997 Gödel Prize in theoretical computer science and the 2009 Dijkstra Prize in distributed computing. From 1997 to 2003, he was editor-in-chief of the Journal of the ACM.^[10] Halpern was also the administrator for the Computing Research Repository, the computer science branch of arXiv.org, and the moderator for the "general literature" and "other" subsections of the repository.^[13,15]

In 1993, Halpern was elected as a Fellow of the Association for the Advancement of Artificial Intelligence (AAAI) for sustained excellence in theoretical research on the logics of and relationships among knowledge, common knowledge, belief and probability.^[9] In 2002, he was inducted as a Fellow (or named a member) of the Association for Computing Machinery, and in 2012 he was selected as an IEEE Fellow.^[11] In 2011, he was awarded a Senior Fellowship of the Zukunftskolleg at the University of Konstanz.^[12] In 2019, Halpern was elected a member of the National Academy of Engineering for methods of reasoning about knowledge, belief, and uncertainty and their applications to distributed computing and multiagent systems. His doctoral students include Nir Friedman, Daphne Koller, and Yoram Moses.^[14] Halpern died on February 13, 2026, at the age of 72.^[4]

Halpern's research revolves around reasoning about knowledge and uncertainty, and its applications to distributed computing, artificial intelligence, computer security, and game theory. He has also contributed to, and continues to be interested in, topics such as fault tolerance in distributed computing, modal logic, causality, program verification, and programming language semantics. His research also has connections with other disciplines, such as economics, mathematics, and philosophy.

Joseph Halpern has written a very large number of articles, as well as two books: Reasoning about Uncertainty and Reasoning About Knowledge.^[17] Among his students are notably Nir Friedman, Daphne Koller, and Yoram Moses.

He is a member of the Association for the Advancement of Artificial Intelligence, the American Academy of Arts and Sciences, the Institute of Electrical and Electronics Engineers, and the Association for Computing Machinery. Joseph Halpern is also an administrator of the computer science section of the ArXiv archive site, and he serves as a moderator for subsections of the site.