Crime and violence are serious issues in informal settlements around the world. To date, there is a dearth of evidence about the causes of and effective strategies for reducing and preventing violence and crime in informal settlements in cities in the Global South. Additionally, women’s voices are often absent from research focused on violence and crime prevention and reduction in informal settlements. The purpose of this study, therefore, was (1) to identify potential causes of violence and crime in informal settlements, as perceived by women living in Mathare informal settlement in Nairobi, Kenya and (2) to highlight residents’ strategies for response and prevention. Fifty-five in-depth and walk-along interviews were conducted with women living in Mathare in 2015-2016. A modified grounded theory approach was used to guide data collection and analysis. The most common contributor to violence and crime identified by women in Mathare was idle youth, but leadership and government challenges, corruption and/or inadequacy of police, community barriers, tribalism, and lack of protective infrastructure also emerged as contributing factors. Despite facing many economic, environmental, and day-to-day challenges, women in Mathare identified violence and crime as predominant issues; thus, developing effective response and prevention strategies to these issues is paramount. Women discussed many strategies and initiatives to reduce and prevent violence and crime in informal settlements, but also identified barriers to implementing them. Findings suggest there is a need for trust-building between formal and informal sectors of the community, systems of accountability, and long-term investment to foster sustainable and effective violence and crime response and prevention in these settlements.