Scientific research indicates that variation in same-sex sexual orientation is normal and part of the spectrum of human sexuality (American Psychological Association [APA], 2021; APA Task Force on Psychological Practice with Sexual Minority Persons, 2021). Despite this evidence, sexual orientation change efforts (SOCE) continue to be provided to adults, children, and adolescents (Green et al., 2020;Mallory et al., 2019). Given the continued practice of SOCE, it is important to review the evidence on its outcomes. In 2009, a comprehensive systematic review of the research on SOCE concluded that these efforts were unsuccessful at changing sexual orientation (APA Task Force on Appropriate Therapeutic Responses to Sexual Orientation [APA Task Force], 2009). Further, the review found harms specific to SOCE (APA Task Force, 2009). Since 2009, number of articles on SOCE have been published in professional journals, but there has not been a thorough review of this literature. This chapter reviews the scientific evidence to date on SOCE. Most of the research and practice is based on sources from the United States, and in certain instances international information is provided.