Background: Adolescent girls and young women (AGYW) in the global south, and particularly in sub-Saharan Africa, continue to be disproportionately impacted by HIV. A complex interplay of biological, individual, social, and structural risk factors put AGYW at three times the risk of acquisition as their male peers. This persistent disparity, coupled with the region’s large and growing youth population, calls for a renewed commitment to effective rights-based HIV prevention approaches. The emergence of oral HIV pre-exposure prophylaxis (PrEP), as well as new options like dapivirine vaginal ring and long-acting injectable cabotegravier, represents an incredible opportunity to address HIV incidence among this population. However, to realize the full potential of these AGYW-controlled HIV prevention methods, a better understanding of the factors that put AGYW at risk of HIV, the extent to which AGYW accurately assess their own risk of HIV, and how that risk assessment effects adherence to daily oral PrEP is needed. Methods: This dissertation comprises three separate studies. The first used data from the Kenya Population-based HIV Impact Assessment Survey (KENPHIA) and latent class analysis to identify underlying patterns of sexual behaviors and sexual partner characteristics among sexually active AGYW, and their relationship to perceived HIV risk. The second also relied on KENPHIA data and logistic regression to examine the accuracy of AGYW’s HIV risk perceptions and the factors may be associated with accurate and inaccurate estimation. The third study drew from data from the Monitoring PrEP in Young Adult Women Study, a randomized control trial among Kenyan AGYW PrEP users to explore the relationship between perceived HIV risk and adherence to daily oral PrEP using moderation analysis. Results: The first study identified three distinct patterns of sexual behavior and sexual partner characteristics, including a minority class characterized by those with older husband and higher alcohol use, that had between 54 and 83 times the odds of HIV acquisition than those in the two majority classes. The second study found that nearly one-third (30.36%) of Kenyan AGYW underestimate their risk of HIV, and that among those determined to be at clinical risk of HIV, the vast majority (80.48%), underestimate their risk. Among all AGYW, those that did not have a recent sex partner, lived in an urban setting, or had greater levels of education were more likely to accurately assess their risk and those with a history of pregnancy were more likely to under-estimate their risk. Among AGYW at clinical risk, only a recent interaction with a health care worker was associated with more accurate risk assessment. The third study revealed low adherence to daily oral PrEP and did not find evidence that the perceived risk of HIV was associated with greater PrEP adherence, as we had hypothesized. Few of the explored factors were associated with PrEP adherence including years of education, objective HIV risk scores, which were negatively associated with PrEP adherence, and disclosure of PrEP use to a sexual partner which was positively associated with PrEP adherence. No statistically significant moderating relationships between perceived HIV risk and PrEP adherence were identified. Conclusions: This research advances understanding of how AGYW in sub-Saharan Africa experience and assess risk of HIV and navigate PrEP use and adherence in response. Findings underscore that in order for the promise of PrEP to be realized among this population, approaches that improve AGYW’s ability to accurately assess their own risk of HIV, and to use that knowledge, even in the face of complex relationship dynamics, are needed. Voluntary- and rights-based approaches that address relational dynamics in AGYW’s sexual lives and support their access to and effective use of PrEP will be critical to realizing the promise of biomedical HIV prevention among this population.