Modified Project Summary/Abstract Section Social and public health restrictions (e.g., physical distancing, school closures) during public health crises are likely impacting the short- and long-term sexual health behaviors of adolescents in the United States (US). These necessary public health measures may be substantially disrupting the provision of and access to sexual health services (i.e., contraception, HIV/STI testing, pre-exposure prophylaxis [PrEP]). Further, emerging evidence underscores the drastic impact of physical distancing measures on sexual behaviors, as well as mental health and substance use. The nascent research in this area has been among adults. It is likely that these effects may be even more pronounced among adolescents given their developmental stage. Youth 13–17 years of age in the US are substantially burdened by sexually transmitted infections (STIs) and unintended pregnancies. Preliminary data suggest that restrictive policies may be having both deleterious effects, including decreased access to STI testing, while also having potentially positive impacts, such as reduced opportunities for condomless sex acts on adolescent sexual health. The effects of restrictive policies on adolescent sexual health behaviors have yet to be systematically investigated, however. Further, these restrictions may be amplifying existing sexual health differences experienced by specific youth. As such, it is particularly critical to understand how the these restrictions are influencing the sexual health of youth facing health differences. To investigate how the social and public health restrictions are impacting the sexual health behaviors of adolescents both in the short- and long-term, we propose to recruit via social media and survey online a longitudinal cohort of 2000 13–17-year-olds from across the US. We will survey youth 12 times over the course of 3.5 years to: (1) Identify the immediate impact of social and public health restrictions on their sexual health behaviors (HIV/STI acquisition; unintended pregnancy; number of penile-vaginal and penile-anal sex acts, respectively; number of condom- and contraceptive-protected sex acts; HIV/STI testing; and PrEP uptake); (2) Identify longitudinal trends in sexual health behaviors as these restrictions change; and (3) Examine how trends vary by important subgroups of youth. Social and public health restrictions have drastically changed the lives of adolescents across the US in a very short amount of time. Understanding how these changes relates to their sexual health behaviors will be critical to continuing to reduce sexual health concerns among adolescents.