Incest is defined, and the literature on it is reviewed. Clinical illustrations focus on the complexity of the issues involved and emphasize the need for careful, long-term, controlled studies using a broad population base for sampling. In addition, the importance of determining clearer and more substantial criteria for psychological assessment is stressed, because the specific impact of incestuous experiences is unclear, multidetermined, and may manifest itself later in life in a variety of ways, including sexual dysfunction and depression.