PROJECT SUMMARY/ABSTRACT Sexual and gender minority (SGM) individuals have higher rates of substance use, mental health disorders, and some physical health conditions. A predominant model for understanding the greater rates of these health conditions among SGM people is the minority stress model, which suggests that increased exposure to enacted and internalized stigma, expectations of prejudice, and identity concealment place additional stress burden on SGM people. Unfortunately, the replicability and rigor of this research is threatened by a lack of validity evidence for the measurement of key minority stress constructs. This is especially problematic for SGM subgroups (e.g., asexual, bisexual, pansexual, queer, non-binary, transfeminine, and transmasculine individuals) and across intersecting identities (e.g., age, race, socioeconomic status, and geographic region) for which the few commonly used measures that exist to measure minority stress are assumed to generalize without adequate validation and measurement invariance testing. This study will address this major methodological gap in SGM health research by establishing validity evidence and measurement equivalence for 3 commonly used measures of minority stress: The Internalized Homophobia Scale- Revised (IHS-R), The Nebraska Outness Scale, and the Minority Stress subscales of the Cultural Assessment of the Risk for Suicide. We will do this by investigating the: convergent and discriminant validity, measurement invariance across SGM subpopulations and intersecting identities and over time, and predictive validity of these measures in explaining substance use across these subpopulations and intersecting identities. This study will lay the groundwork for rigorous and replicable SGM health research.