Background and aims: Intimate partner violence (IPV) has emerged as a serious public health issue that demands global action. While practitioners and researchers in the violence field have long argued that gender-related norms are fundamentally linked to IPV, there is little theoretical understanding of exactly how norms affect violence in practice. Moreover, while norms are central to feminist accounts of violence, there has been little effort to apply social norms theory to the realities of partner violence. This thesis aims to address these gaps by investigating empirically how social norms affect partner violence, using Tanzania as a case study. Methods: In particular, this study employs a qualitative methodology and uses two sources of data – focus group discussions and semi-structured interviews – to generate data on how local people in an urban community in Mwanza, Tanzania describe norms linked to IPV. While the interview guides are structured to probe elements of social norm theory, the questions are open-­‐ended to encourage participants to speak to their own understandings of IPV. Similarly, whereas the study primarily uses social norms theory to interpret its findings, it draws on other bodies of social science theory, such as gender theory, to fully account for how norms perpetuate IPV, as revealed by the data. Findings and conclusion: The study concludes that whereas traditional norms theory offers insights useful for identifying normative influence, it is inadequate for understanding the role of gender norms in catalysing and sustaining IPV. To fill this gap, the study unites disparate bodies of scholarship into a coherent framework for articulating how gender norms affect IPV in low-­‐income countries contextually similar to Tanzania. Because such a framework is embedded in empirical realities, it also has utility for donors and programmers wishing to employ it to design and evaluate programmes aimed at transforming gender discriminatory norms that sustain IPV in similar settings.