Adolf Otto Reinhold Windaus (December 25, 1876 – June 9, 1959) was a German chemist who won a Nobel Prize in Chemistry in 1928 for his work on sterols and their relation to vitamins. He was the doctoral advisor of Adolf Butenandt who also won a Nobel Prize in Chemistry in 1939.

Adolf Windaus was born in Berlin. His interest in chemistry was raised by lectures of Emil Fischer. He started studying medicine and chemistry in Berlin and later in Freiburg. He got his PhD in early 1900 and focused on cholesterol and other sterols at the University of Freiburg. In 1913 he became professor for chemistry at the University of Innsbruck and in 1915 he changed to the University of Göttingen where he stayed until his retirement in 1944.

He was involved in the discovery of the transformation of cholesterol through several steps to vitamin D₃ (Cholecalciferol). He gave his patents to Merck and Bayer and they brought out the medical Vigantol in 1927.