Joseph Nicolosi (born January 21, 1947) is an American clinical psychologist, founder and director of the Thomas Aquinas Psychological Clinic in Encino, California, and a founder and former president of the National Association for Research and Therapy of Homosexuality (NARTH). Nicolosi has advocated and practiced reparative therapy, a practice that he claims can help people overcome or mitigate their homosexual desires and replace them with heterosexual ones.Nicolosi has described his theories in Reparative Therapy of Male Homosexuality: A New Clinical Approach and three other books. Nicolosi proposes that homosexuality is often the product of a condition he describes as gender-identity deficit caused by an alienation from, and perceived rejection by, individuals of the subject's gender. He holds a Ph.D. from the California School of Professional Psychology.