Psychology’s understanding of lesbian, gay, and bisexual (LGB) people has evolved, become more refined, and impacted the lives of LGB people in profound ways. This chapter traces the history of LGB psychology from the nineteenth century to the present and focuses on major events and the intersections of theory, psychological science, politics, and activism in the history of this field. It explores various facets of cultural and psychological history that include the pathologizing of homosexuality, the rise of psychological science and the political movements in the mid-twentieth century, and the major shifts in policy that ensued. The toll of the AIDS epidemic on the field is discussed as is the impact of psychological research on national and international policy and legislation.