**Carl Wilhelm Oseen** (17 April 1879, Lund – 7 November 1944, Uppsala) was a theoretical physicist in Uppsala and Director of the Nobel Institute for Theoretical Physics in Stockholm.

Oseen was born in Lund, and took a Fil. Kund. degree at Lund University in 1897.

Oseen formulated the fundamentals of the elasticity theory of liquid crystals (Oseen elasticity theory), as well as the Oseen equations for viscous fluid flow at small Reynolds numbers. He gave his name to the Oseen tensor and, with Horace Lamb, to the Lamb–Oseen vortex. The Basset–Boussinesq–Oseen (BBO) equation describes the motion of – and forces on – a particle moving in an unsteady flow at low Reynolds numbers.

Oseen was a member of the Royal Swedish Academy of Sciences from 1921, and a member of the Academy's Nobel Prize committee for physics from 1922. As a full professor of a Swedish university, Oseen also had the right to nominate Nobel Prize winners.

It was Oseen who nominated Albert Einstein for the Nobel Prize in 1921, for Einstein's work on the photoelectric effect (rather than the more controversial theory of general relativity). Einstein was finally awarded the prize for 1921 when Oseen repeated the nomination in 1922.