Sir Ernst Boris Chain (19 June 1906 – 12 August 1979) was a German-born British biochemist and co-recipient of the Nobel Prize in Physiology or Medicine for his work on penicillin.

After a couple of months he was accepted as a PhD student at Fitzwilliam College, Cambridge, where he began working on phospholipids under the direction of Sir Frederick Gowland Hopkins.

During this time he worked on a range of research topics, including snake venoms, tumour metabolism, lysozymes, and biochemistry techniques.

Along with Edward Abraham he was also involved in theorising the beta-lactam structure of penicillin in 1942,[17] which was confirmed by X-ray crystallography done by Dorothy Hodgkin in 1945.

Towards the end of World War II, Chain learned his mother and sister had been killed by the Nazis.

He returned to Britain in 1964 as the founder and head of the biochemistry department at Imperial College London, where he stayed until his retirement, specialising in fermentation technologies.

In spite of his successful scientific career and widespread recognition from his Nobel Prize, Chain was for some time barred from entry to the United States under the McCarran Internal Security Act of 1950, being declined a visa on two occasions in 1951.