Urbanization has a complex relationship with injury. The movement of people from rural to urban areas, and their accumulation in cities, changes the risk of injury and its causes. Particularly in developing countries, urbanization exposes people to a host of dangers they often do not encounter in rural areas. It does this through two primary means. In a general sense, urbanization in low- and middle-income countries (LMICs) is often unplanned and rapid, overwhelming urban infrastructure and its margin of safety. Urbanization outpacing its infrastructure is a major determinant of urban road crashes, for example. Additionally, rapid urbanization often results in great social inequality, with many people living in informal settlements or other substandard housing and working in conditions that are not conducive to safety. Combined with the weak safety enforcement and limited resources for prevention and treatment of injuries, residents of urban LMIC areas often face unacceptably high injury risks. While innovation to prevent injury has lagged behind that of many other LMIC public health priorities, there exist low-cost approaches to prevent injury in urbanized and urbanizing areas—especially for road crashes. There remains an urgent need to adapt models of prehospital and hospital-based trauma care to urban LMIC areas.