Paul Donald MacLean (May 1, 1913 – December 26, 2007) was an American physician and neuroscientist who made significant contributions in the fields of physiology, psychiatry, and brain research through his work at Yale Medical School and the National Institute of Mental Health.

During his service with Yale's 39th General Hospital Brigade in New Zealand, MacLean worked together with Dr. Averill Liebow to show that the diphtheria bacillus was a cause of tropical ulcers, paving the way for successful prophylaxis and treatment.

After leaving the Army in 1946, MacLean practiced medicine in Seattle, and held a clinical appointment at the University of Washington Medical School.

From 1947 to 1949, MacLean was a United States Public Health Service Fellow at Harvard Medical School/Massachusetts General Hospital, studying with Dr. Stanley Cobb.

During this time, MacLean did research on psychomotor epilepsy, and published his paper on the "visceral brain", for which he introduced the term "limbic system" in 1952).