Léon Rosenfeld (French: [ʁɔzɛnfɛld]; 14 August 1904 in Charleroi – 23 March 1974^[1]) was a Belgian physicist and Marxist.

Rosenfeld was born into a secular Jewish family. He was a polyglot who knew eight or nine languages and was fluent in at least five of them.^[2]

Rosenfeld obtained a PhD at the University of Liège in 1926, and he was a close collaborator of the physicist Niels Bohr. Rosenfeld published in 1930 the first systematic Hamiltonian approach to Lagrangian models that possess a local gauge symmetry, which predates by two decades the work by Paul Dirac and Peter Bergmann.^[3] Rosenfeld contributed to a wide range of physics fields, from statistical physics and quantum field theory to astrophysics.^[2] Along with Frederik Belinfante, he derived the Belinfante–Rosenfeld stress–energy tensor. He also founded the journal Nuclear Physics and coined the term lepton.^[4]

In 1933, Rosenfeld married Yvonne Cambresier, who was one of the first women to obtain a Physics PhD from a European university. They had a daughter, Andrée Rosenfeld (1934–2008) and a son, Jean Rosenfeld.^[5]

Rosenfeld held chairs at multiple universities: Liège, Utrecht, Manchester, and Copenhagen.^[2]

In 1949 Léon Rosenfeld was awarded the Francqui Prize for Exact Sciences.^[2]

• Rosenfeld, Léon (1948). Nuclear Forces. North-Holland.
• Rosenfeld, Léon (1951). Theory Of Electrons. North-Holland.
• Bohr, Niels; Rosenfeld, Léon (1933). "Zur Frage der Messbarkeit der elektromagnetischen Feldgrössen" [On the Question of the Measurability of Electromagnetic Field Quantities]. Royal_Danish_Academy_of_Sciences_and_Letters (in German): 123–166 – via Translated from German (1996) Niels Bohr Collected Works. Vol. 7. North–Holland: Amsterdam. Demonstrated the logical consistency of quantum electrodynamics.