Ernst Wilhelm Theodor Trendelenburg (16 July 1877 – 16 March 1946) was a German physiologist known for his work in physiological optics. He studied physiology at the University of Freiburg, receiving his doctorate from the University of Leipzig in 1900. He worked as an assistant to Johannes von Kries at Freiburg and to Ewald Hering at Leipzig. In 1904 he obtained his habilitation for physiology at Freiburg, and in 1911 became a full professor at the University of Innsbruck. Afterwards, he held professorships at the universities of Giessen (from 1916), Tübingen (from 1917) and Berlin (from 1927).