Dirk ter Haar (Oosterwolde, 19 April 1919 – Drachten, 3 September 2002) was an Anglo-Dutch physicist.
Dirk ter Haar (Dr., B.Sc., M.Sc., MA, D.Sc., FRSE) studied physics at Leiden University, was research fellow of Niels Bohr in Copenhagen, and received his Ph.D. in Leiden from Hendrik Kramers for a dissertation on the origin of the solar system. In 1949 he became professor of physics at the University of St. Andrews and in 1950 he emigrated to England, where he later became a British citizen. He became a Fellow of Magdalen College and reader in theoretical physics at the University of Oxford.
In 1966 Ter Haar became a corresponding member of the Royal Netherlands Academy of Arts and Sciences.
Many prominent scientists studied under ter Haar, including Anthony Leggett, winner of the Nobel Prize in Physics in 2003 and Deng Jiaxian, one of the leading scientists and founders of Chinese nuclear weapon programs.
He wrote numerous books on physics, such as Elements of Statistical Mechanics. In addition, he wrote a book on Kramers and was an editor for Physics Letters (later Physics Letters A). In 1984 the book Essays in Theoretical Physics in honour of Dirk ter Haar was published in honour of his work in statistical physics and quantum mechanics.