Gender inequity is pervasive globally and is an upstream determinant of a wide range of poor health outcomes for women and girls, including gender-based violence, HIV, reproductive health, child marriage, and female genital cutting. Social norms that uphold gender inequity are, thus, a primary upstream determinant of these poor health outcomes. Critical gaps in the research evidence exist around how to measure social norms related to gender equity, how to change these norms, and how changes in these norms may lead to change in gender equity-related behavior. This dissertation contributes to the growing body of research on gender equity and related social norms, and how public health interventions can improve health outcomes related to gender inequity. Data from a four-arm cluster randomized control trial of the Reaching Married Adolescents in Niger (RMA) intervention conducted among married adolescent girls and their husbands in the Dosso region of Niger were utilized in this dissertation research. The RMA intervention aimed to increase modern contraceptive use and decrease intimate partner violence (IPV) via trained community health worker approaches, including household visits and small group discussions, with both married adolescent girls and their husbands. Chapter 1 of this dissertation contributes to the field of IPV prevention an in-depth psychometric assessment of a novel scale that measures perceived social norms regarding IPV and reproductive coercion. Evidence of reliability and validity, as well as validating associations with IPV perpetration behavior, provided by this research contribute to the value and utility of this scale for monitoring and evaluating change in social norms related to IPV. Chapter 2 provides evidence that the RMA small group intervention reduced inequitable gender norms after 12 months of receiving the program, and that the RMA household visit intervention may have increased inequitable gender norms. These results from a rigorous evaluation are among very few evaluations of gender norm-focused public health interventions demonstrating effects on social norms. Furthering this finding, Chapter 3 offers a mediation analysis using modern causal inference methods that yielded evidence of social norms change being an important mechanism behind observed reductions in IPV for the small group intervention. This chapter also raises important questions about the mechanism behind increases in modern contraceptive use associated with the RMA household visits and combination interventions, as social norms appear to have not been an important mediator. These results are one of very few, if any, studies to demonstrate social norms change as a mechanism behind an intervention’s effects on IPV in low and middle income countries, strengthening the evidence behind theories and frameworks that postulate the importance of social norms for behavior change. In order to meet the Sustainable Development Goals 2030 in the next eight years, there is an urgent need to expand the evidence-base on how to increase gender equity within societies. This dissertation contributes two practical tools for researchers and practitioners to work toward these goals: 1) a brief valid and reliable scale for measuring social norms related to IPV and reproductive coercion and 2) evidence that the RMA small group intervention model affects inequitable gender norms and, in turn, IPV. Such contributions offer critical evidence to further inform the promotion of gender equity via changing social norms, efforts that are essential to reducing the health burden of gender inequity on women and girls globally.