Joe Halpern is a professor of computer science. His research focuses on the interface between game and decision theory and computer science, on reasoning about knowledge and uncertainty, and on causality. He has also done work on and continues to think actively about security, (fault tolerant) distributed computing, and modal logic. His work lies at the boundary of a number of fields. He said, "I once gave a talk in the economics department at Princeton where I described myself as someone with a Ph.D. in mathematics, who calls himself a computer scientist, and is giving a talk to economists about a subject mainly studied by philosophers. That's probably the best one-sentence description I can give."