In 1920, John Watson and Rosalie Rayner claimed to have conditioned a baby boy, Albert, to fear a laboratory rat. In subsequent tests, they reported that the child's fear generalized to other furry objects. After the last testing session, Albert disappeared, creating one of the greatest mysteries in the history of psychology. This article summarizes the authors' efforts to determine Albert's identity and fate. Examinations of Watson's personal correspondence, scientific production (books, journal articles, film), and public documents (national census data, state birth and death records) suggested that an employee at the Harriet Lane Home was Albert's mother. Contact with the woman's descendents led the authors to the individual they believe to be "Little Albert."