The time has arrived for psychological science to translate the accumulating empirical research regarding sexual and gender minority (SGM) mental health into evidence-based affirmative treatments for this population. Far from the unscientific, homophobic theories of the early 20th century, several recent efforts in psychological science are starting to pave the way for evidence-based SGM-affirmative mental health treatments. These efforts include (a) identifying clear treatment targets for SGM, (b) conducting treatment studies that test the efficacy of therapy for SGM populations, (c) increased reporting of sexual orientation and gender diversity in existing randomized controlled trials conducted with the general population, and (d) reducing stigma itself, which has heretofore impeded the resources necessary to produce scientific evidence about SGM-affirmative treatments. This article reviews this progress and outlines future research directions needed to advance evidence-based practice for SGM, including determining whether and how existing evidence-based treatments need to be adapted to address SGM-specific concerns, why SGM-affirmative treatments work, and for whom and under what conditions SGM-affirmative treatments work best. A program of research is described that attempts to address these questions through randomized controlled trials with strong comparison conditions, psychotherapy process research of current SGM-affirmative practice, and tests of treatment moderators. To the extent that the mental health profession continues to pursue these solutions, it can ensure the continued flourishing of this population, whose visibility and vibrancy likely represent the surest route toward improving public acceptance and therefore its future mental health. (PsycINFO Database Record (c) 2018 APA, all rights reserved).