Critical time intervention (CTI) is a time-limited, evidence-based model of care coordination for people that is delivered during a critical period of transition in their lives, such as the transition from shelters, hospitals, jails, and prisons into the community. This, in turn, places them at risk of ongoing instability and return to homelessness, re-institutionalization and other adverse outcomes. CTI provides direct emotional and practical assistance and strengthens individuals' ties to their community and support systems during the critical time. On the strength of numerous tests of its impact (including several randomized trials) the model has been widely implemented in the US, Europe, and Latin America as many communities struggle to devise effective responses to homelessness and dislocation among their most vulnerable citizens. The book recounts CTI's initial development by a creative team of mental health and social service providers working in large homeless shelters in New York City during the early years of the city's contemporary homelessness crisis, describes the main components of the model, emphasizing how it differs from standard forms of case management, summarizes research evidence supporting the effectiveness of CTI, describes how the model has been adapted for use with different high-need populations in a variety of settings in the US an elsewhere, and considers strategies and challenges related to broader implementation of CTI including workforce training, funding, fidelity assurance, and program drift. It concludes with a consideration of the implications of CTI for the design of new "time-sensitive" intervention models in social work and allied fields.