Erwin Finlay-Freundlich (May 29, 1885 - July 24, 1964) was a German astronomer, a pupil of Felix Klein. He was born in Biebrich, Germany. Freundlich was a working associate of Albert Einstein and introduced experiments for which the general theory of relativity could be tested by astronomical observations based on the gravitational redshift.

After finishing his thesis with Felix Klein at the University of Göttingen in 1910, he became assistant at the Observatory in Berlin, where he became associated with Einstein. During a solar eclipse expedition in 1914 to verify general relativity World War I broke out and he was interned in Russia. After the war, he was engaged in construction of a solar observatory in Potsdam, the Einsteinturm, and he was director of the Einstein Institut. In 1933 he left Germany and was appointed professor at the University of Istanbul, which was reformed by Kemal Atatürk with the help of many German scholars. His appointment at the Charles University of Prague was terminated by the German occupation. On the recommendation of Arthur Stanley Eddington he went to St. Andrews University in Scotland. From 1951 to 1959 he was John Napier professor of Astronomy. On his retirement he returned to his native town Wiesbaden and was appointed professor at the University of Mainz. Freundlich died in Wiesbaden, Germany.

Freundlich researched the deflection of light rays passing close to the Sun. He proposed an experiment, during an eclipse, to verify the validity of Einstein's theory of general relativity. Freundlich's demonstration would have proven Newton's theories incorrect. He did conduct inconclusive tests on the prediction by Einstein's theory of gravitation-induced red shift of spectral lines in the Sun, using the solar observatories he had constructed in Potsdam and Istanbul. In 1953 he proposed with Max Bornan an alternative explanation of the red shifts observed in galaxies by a tired light model.