Flora Rheta Schreiber (April 24, 1918 – November 3, 1988) was an American journalist and the author of the 1973 bestseller Sybil. For many years, she served as an English instructor at John Jay College of Criminal Justice.

Her groundbreaking book, Sybil (1973), reveals the life of a woman, later identified as Shirley Ardell Mason, who was diagnosed with dissociative identity disorder and alleged to have 16 different personalities. The pseudonym Sybil Isabel Dorsett was used to conceal Mason's identity, in accordance with her wish for privacy. Schreiber's work unveiled the complexities of mental health and its impact on individuals and their families, contributing significantly to the public's understanding of such disorders.

Later, she documented the chilling story of Joseph Kallinger in her book The Shoemaker, which detailed the life of a serial killer diagnosed with paranoid schizophrenia. This work further established Schreiber as a significant figure in the exploration of psychological disorders through literature.

Flora Rheta Schreiber's papers are preserved in the Special Collections unit at Lloyd Sealy Library of John Jay College, offering a comprehensive view of her life and career.