Adolf Eugen Fick (3 September 1829 – 21 August 1901) was a German-born physician and physiologist.

Fick began his work in the formal study of mathematics and physics before realising an aptitude for medicine.

In 1870, he was the first to measure cardiac output, using what is now called the Fick principle.

Fick managed to double-publish his law of diffusion, as it applied equally to physiology and physics.

His work led to the development of the direct Fick method for measuring cardiac output.