John David Jackson (January 19, 1925 – May 20, 2016) was a Canadian–American theoretical physicist. He was a professor at the University of California, Berkeley and a faculty senior scientist emeritus at Lawrence Berkeley National Laboratory.

Jackson was a member of the National Academy of Sciences and was well known for his work in nuclear and particle physics, as well as his widely used graduate text on classical electrodynamics.

Born in London, Ontario, Canada, Jackson attended the University of Western Ontario, receiving a B.Sc. in honors physics and mathematics in 1946. He went on to graduate study at MIT, where he worked under Victor Weisskopf, completing his Ph.D. thesis in 1949.

Jackson held academic appointments successively at McGill University, thanks to Philip Russell Wallace, a prominent Canadian theoretical physicist, (January 1950 – 1957); then the University of Illinois at Urbana–Champaign (1957–1967); and finally the University of California, Berkeley (1967–1995). At McGill, he was Assistant and Associate Professor of Mathematics; at Illinois and Berkeley, he was in the Physics Departments. At the latter, he held appointments on campus and at the Lawrence Berkeley National Laboratory. After retiring from teaching in 1993, he continued to be active at LBNL.

At McGill in the 1950s, in addition to appreciable teaching, Jackson found time for research on atomic processes and nuclear reactions at intermediate energies and the beginnings of his book on classical electricity and magnetism.

While on leave at Princeton University, he found a fruitful collaboration with Sam Treiman and H. W. Wyld on weak interactions, particularly the various observable decay correlations in allowed nuclear beta decay involving the electron's momentum, its spin, the neutrino's momentum, and the nuclear spin that provide information about parity conservation or non-conservation and time reversal conservation or not. He also published an early paper on the theoretical foundation for the then recently discovered muon-catalyzed fusion of hydrogen isotopes.

While at the University of Illinois (1957–1967) Jackson initially continued work on weak interactions as well as strange particle interactions at low energy with Wyld and others. On sabbatical leave at CERN in 1963–64, he collaborated with Kurt Gottfried on production and decay of unstable resonances in high-energy hadronic collisions. They introduced the use of the density matrix to connect production mechanisms to the decay patterns and described the influence of competing processes ("absorption") on the reactions.

During this period Jackson lectured at three summer schools—on dispersion relations at the first Scottish Universities Summer School in Physics, 1960; on weak interactions at the Brandeis Summer Institute, 1962; and on particle and polarization decay distributions at the Summer School of Theoretical Physics, Les Houches, 1965. He also published three books, one on particle physics, based on lectures at the Canadian Summer School in Edmonton and Jasper, 1957; the second, a small book on mathematics for quantum mechanics (1962) and the third, also in 1962, the first edition of his text on classical electrodynamics. The book is notorious for the difficulty of its problems, and its tendency to treat non-obvious conclusions as self-evident. Jackson's high standards and admonitory vocabulary are the subject of an amusing memorial volume by his son Ian Jackson.