Jon Elster (/ˈɛlstər/; born 22 February 1940) is a Norwegian philosopher and political theorist who holds the Robert K. Merton professorship of Social Science at Columbia University and since 2005 professor of social science at the Collège de France.

He received his PhD in social science from the École Normale Superieure in 1972. He has previously taught at the University of Paris, the University of Oslo, and the University of Chicago, where he became professor of political science in 1984. Since 1995, he has held the Robert K. Merton professorship of Social Science at Columbia University, as well as being professor of social science at the Collège de France since 2005.

Elster has authored works in the philosophy of social science and rational choice theory. He is also a notable proponent of analytical Marxism, was a leading member of the September Group, which attempted to reinterpret Marxism on the basis of analytic philosophy, and a critic of neoclassical economics and public choice theory, largely on behavioral and psychological grounds. In 2016, he was awarded the 22nd Johan Skytte Prize in Political Science for his contributions to political science.

Elster is the son of journalist/author and CEO of the Norwegian Broadcasting Corporation Torolf Elster, and poet Magli Elster. He earned his PhD in 1972 from the École Normale Superieure in Paris with a dissertation on Karl Marx under the direction of Raymond Aron. Elster was a member of the September Group for many years but left in the early 1990s. Elster previously taught at the University of Oslo in the department of history and held an endowed chair at the University of Chicago, teaching in the departments of philosophy and political science. He is now Robert K. Merton Professor of Social Sciences with appointments in Political Science and Philosophy at Columbia University and professeur honoraire at the Collège de France. He was awarded the Jean Nicod Prize in 1997, the John von Neumann Award in 2002, and the Skytte Prize in Political Science in 2016.

He is a member of the Norwegian Academy of Science and Letters. He is also a member of the American Academy of Arts and Sciences, of the American Philosophical Society, of the Academia Europaea, and a Corresponding Fellow of the British Academy.

Elster is doctor honoris causa at the universities of Valencia, Stockholm, Oslo, Trondheim (NTNU), Louvain-la-Neuve, Torcuato di Tella, and the National University of Colombia. He is honorary professor at the University of Chongqing.

Much of Elster's writing is characterized by attempts to use analytical theories, especially rational choice theory, as a springboard for philosophical and ethical analysis, with numerous examples from literature and history. "Elster has made important contributions to several fields," Daniel Little wrote in a review essay. "The breadth and depth of his writings are striking in a time of high specialisation; he is read and discussed by political scientists, legal scholars, economists and philosophers. His work is difficult to summarise in a slogan, but ... it is generally informed by a broad and deep acquaintance with relevant literature in economics, political science, history, philosophy, and psychology."

A student of the philosophy of social science (a topic he investigated through case studies in Explaining Technical Change), Elster strongly argued that social scientific explanations had to be built on top of methodological individualism (the belief that only individuals, not larger entities like "organizations" or "societies", can actually do things) and microfoundations (explaining big societal changes in terms of individual actions). He criticized Marxists and other social scientists for believing in functionalism (the belief that institutions exist because of their effect on society) and instead tried to give Marxism a foundation in game theory (the economic notion that people make choices based on the expected benefits and the choices others are likely to make).