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

[3] 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.

He also founded the journal Nuclear Physics and coined the term lepton.

[5] In 1933, Rosenfeld married Yvonne Cambresier, who was one of the first women to obtain a Physics PhD from a European university.

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