The growth and impact of urban environmental problems can manifest as significant stress and eventual crises for cities and their residents. The focus of this chapter is on how and why these stressors and crises are addressed in cities and the conditions under which the crises can eventually result in significant environmental policy transitions and follow-on transformations. Several different types of documented urban crises (including ecological-resource, urban spatial development, socio-economic, and extreme events) are discussed and analyzed in the chapter. Social, environmental/ecological, and infrastructural/technological drivers influence the connection between urban environmental stress, crisis, transition, and transformation. The actual mechanisms that set up and orchestrate the transition process reflect the resilience of the existing environmental and policy management regime and the magnitude of the stress and crisis. The chapter focuses on describing each of the steps in the transition and the mechanisms that connect each step, as well as the key terms and concepts associated with the process. The importance of policy system tipping points or regime shifts is illustrated.