Harry Bateman FRS (29 May 1882 – 21 January 1946) was an English mathematician with a specialty in differential equations of mathematical physics. With Ebenezer Cunningham, he expanded the views of spacetime symmetry of Lorentz and Poincare to a more expansive conformal group of spacetime leaving Maxwell's equations invariant. Moving to the US, he obtained a Ph.D. in geometry with Frank Morley and became a professor of mathematics at California Institute of Technology. There he taught fluid dynamics to students going into aerodynamics with Theodore von Karman. Bateman made a broad survey of applied differential equations in his Gibbs Lecture in 1943 titled, "The control of an elastic fluid".

Bateman was born in Manchester, England, on 29 May 1882. He first gained an interest in mathematics during his time at Manchester Grammar School. In his final year, he won a scholarship to Trinity College, Cambridge. Bateman studied with coach Robert Alfred Herman to prepare for the Cambridge Mathematical Tripos. He distinguished himself in 1903 as Senior Wrangler (tied with P.E. Marrack) and by winning the Smith's Prize (1905).

His first paper, "The determination of curves satisfying given conditions", was published when he was still an undergraduate student. He studied in Göttingen and Paris, and taught at the University of Liverpool and University of Manchester. After moving to the US in 1910, he taught at Bryn Mawr College and then Johns Hopkins University. There, working with Frank Morley in geometry, he achieved his Ph.D., prior to which he had already published more than 60 papers, including some of his celebrated papers. In 1917, he took up his permanent position at the California Institute of Technology, which was then known as the "Throop Polytechnic Institute".

Eric Temple Bell says, "Like his contemporaries and immediate predecessors among Cambridge mathematicians of the first decade of this century [1901–1910]... Bateman was thoroughly trained in both pure analysis and mathematical physics, and retained an equal interest in both throughout his scientific career."

Theodore von Kármán was called in as an advisor for a projected aeronautics laboratory at Caltech and later gave this appraisal of Bateman:

In 1926 Cal Tech [sic] had only a minor interest in aeronautics. The professorship that came nearest to aeronautics was occupied by a shy, meticulous Englishman, Dr. Harry Bateman. He was an applied mathematician from Cambridge who worked in the field of fluid mechanics. He seemed to know everything but did nothing important. I liked him.

Harry Bateman married Ethel Horner in 1912 and had a son named Harry Graham, who died as a child. Later, the couple adopted a daughter named Joan Margaret. He died on his way to New York in 1946 of coronary thrombosis.

In 1907, Harry Bateman was lecturing at the University of Liverpool together with another senior wrangler, Ebenezer Cunningham. In 1908, together they came up with the idea of a conformal group of spacetime (now usually denoted as C(1,3)) which involved an extension of the method of images.