Arthur John Birch, AC CMG FRS FAA (3 August 1915 – 8 December 1995) was an Australian organic chemist.
Birch developed the Birch reduction of aromatic rings (by treatment with lithium metal and ammonia) which is widely used in synthetic organic chemistry. The Birch Reduction enables the modification of steroids. In 1948 Birch published the first total synthesis of a male sex hormone (19-nortestosterone), as the first member of a new structural series. This series later comprised the first oral contraceptive pill, which was made by others. The Birch reduction also allows for the development of other steroid drugs and antibiotics – he also made the first simple synthesis of the ring A-B structure of cholesterol. Birch published over 440 scientific papers and reports.