Roger Yonchien Tsien (February 1, 1952 – August 24, 2016) was an American biochemist. He was a professor of chemistry and biochemistry at the University of California, San Diego and was awarded the Nobel Prize in Chemistry for his discovery and development of the green fluorescent protein, in collaboration with organic chemist Osamu Shimomura and neurobiologist Martin Chalfie. Tsien was also a pioneer of calcium imaging.