PROJECT SUMMARY. Sexual and gender minority (SGM) youth, inclusive of lesbian, gay, bisexual, transgender, and queer are more likely to initiate vaping and currently vape than non-SGM youth in the United States. Vaping significantly increases the risks of initiating cigarette smoking and poly-tobacco use, and consequently tobacco-related illnesses. Higher prevalence of vaping among SGM youth will therefore widen tobacco-related health disparities later in life. anti-vaping campaigns designed for the general youth population may not fully address SGM youths' underlying beliefs and attitudes toward vaping. There is a critical gap in research on evidence- based and culturally tailored interventions to reduce vaping initiation in the SGM youth population. Our long- term goal is to reduce tobacco use and tobacco-related health disparities among SGM populations. The objective of Project SMART (Social Media Anti-vaping Messages to Reduce ENDS Use Among Sexual and Gender Minority Teens) is to evaluate the effectiveness of an SGM-tailored social media intervention to prevent vaping initiation among SGM youth ages 13-18 years. Our central hypothesis is that culturally tailored anti-vaping social media messages will be more effective than non-tailored messages to prevent vaping initiation among SGM youth. The scientific premise for this work is based on the principles of cultural tailoring in health communication for vulnerable populations, the Health Equity Promotion Model, and the Message Impact Framework. We are developing and evaluating a social media intervention because SGM youth have a high rate of social media use and are more likely to go online for health information than non-SGM youth. Social media, moreover, are increasingly used for health promotion to address health disparities and well- being of SGM populations. Our specific aims are: 1) Explore salient beliefs and cultural tailoring preferences related to vaping initiation among SGM youth to inform the development of social media anti-vaping messages, 2) Identify promising anti-vaping messages and cultural tailoring strategies to reduce vaping initiation among SGM youth, and 3) Evaluate the effectiveness of repeated exposure to SGM-tailored anti-vaping social media messages on subsequent vaping initiation among SGM youth. We are developing and evaluating a culturally tailored social media intervention using qualitative research methods and survey experiments. We will conduct rapid-cycle feedback with stakeholders including SGM organization leaders to provide input on the message design, testing, and intervention implementation to ensure feasibility and acceptability of the intervention. Impact: Findings will provide evidence for the comparative effectiveness of an SGM-tailored anti-vaping social media intervention to reduce vaping initiation among SGM youth versus non-tailored messages. The study findings and approach will inform efforts to reduce disparities in vaping among SGM and other vu...