Most stakeholders interested in ending chronic homelessness are familiar with the recently published cost avoidance analysis conducted for the New York/New York Initiative hereafter, “NY/NY analysis.” The NY/NY analysis looked at the NY/NY Initiative, which placed homeless individuals with serious mental illness (SMI) in a variety of permanent supportive housing (PSH) arrangements, and helped them stay there. It examined three issues—changed use of public services, changed costs resulting from the changed use, and savings (whether PSH cost the same or less than pre-PSH use of public services). The Corporation for Supportive Housing (CSH) promoted the NY/NY analysis because it thought the results might provide powerful evidence of supportive housing’s ability to produce outcomes that policy makers want—reductions in inappropriate use of emergency public services, and their associated costs. The results fulfilled these hopes, showing significant savings. Together with evidence that PSH is able to attract and retain chronically homeless disabled people (Shern et al., 1997; Tsemberis and Eisenberg, 2000) and that the probable number of such people is small enough to be a feasible policy target (about 200,000 to 250,000 nationally), the NY/NY analysis has galvanized many cities and the country as a whole to adopt the goal of ending chronic homelessness. (Author)