JASON is an independent group of elite scientists who advise the United States government on matters of science and technology, mostly of a sensitive nature. The group was created in the aftermath of the Sputnik launch as a way to reinvigorate the idea of having the nation's preeminent scientists help the government with defense problems, similar to the way that scientists helped in World War II but with a new and younger generation. It was established in 1960 and has somewhere between 30 and 60 members. Its work first gained public notoriety as the source of the Vietnam War's McNamara Line electronic barrier. Although most of its research is military-focused, JASON also produced early work on the science of global warming and acid rain. Current unclassified research interests include health informatics, cyberwarfare, and renewable energy.

For administrative purposes, JASON's activities are run through the MITRE Corporation, a not-for-profit corporation in McLean, Virginia, which operates Federally Funded Research and Development Centers (FFRDCs) for the federal government. The Department of Defense ended its contract with MITRE in April 2019, effectively cutting ties with JASON. However, due to the efforts of the Department of Energy as well as others within the government, to include an act of Congress, the contract was reinstated and is now again with the Department of Defense.

JASON typically performs most of its work during an annual summer study. Its sponsors include the Department of Defense, the Department of Energy, and the U.S. Intelligence Community. Most of the resulting JASON reports are classified.

The name "JASON" is sometimes explained as an acronym, standing either for "July August September October November", the months in which the group would typically meet; or, tongue in cheek, for "Junior Achiever, Somewhat Older Now". However, neither explanation is correct; in fact, the name is not an acronym at all. Mildred Goldberger, wife of group member Murph Goldberger, disliked the name given by the Pentagon, Project Sunrise, and suggested the group be named Jason, inspired by the mythological character Jason. JASON studies have included a now-mothballed system for communicating with submarines using extremely long radio waves (Project Seafarer, Project Sanguine), an astronomical technique for overcoming the atmosphere's distortion (adaptive optics), the many problems of missile defense, technologies for verifying compliance with treaties banning nuclear tests, a 1979 report describing CO₂-driven global warming, and the McNamara Line's electronic barrier, a system of computer-linked sensors developed during the Vietnam War which became the precursor to the modern electronic battlefield.

Among the more recent activities was a non-consensus-commensurate (in other words, providing a view alternative to the prevailing one in the federal executive department which commissioned the report), and now declassified, report to the State Department dismissing sounds associated with the Havana syndrome cases as caused by crickets as opposed to microwave weapons. This was followed by a 2021 report, in which JASON again found no compelling evidence that the anomalous health incidents were caused by a deliberate attack using a radio-frequency or any other directed energy weapon.

JASON members, known informally as "Jasons," include physicists, biologists, chemists, oceanographers, mathematicians, and computer scientists, predominated by theoretical physicists. They are selected by current members, and, over the years, have included eleven Nobel Prize laureates and several dozen members of the United States National Academy of Sciences. Claire Ellen Max was the first female scientist invited to join in 1983. All members have a wide range of security clearances that allow them to do their work.

The founders of JASON include John Wheeler and Charles H. Townes. Other early members included Murray Gell-Mann, S. Courtenay Wright, Robert Gomer, Walter Munk, Hans Bethe, Nick Christofilos, Fredrik Zachariasen, Marshall Rosenbluth, Ed Frieman, Hal Lewis, Sam Treiman, Conrad Longmire, Steven Weinberg, Roger Dashen, and Freeman Dyson.

Some Nobel Prize-winning members of JASON include Donald Glaser, Val Fitch, Murray Gell-Mann, Luis Walter Alvarez, Henry Way Kendall, and Steven Weinberg.