The COVID-19 pandemic has strained an ongoing housing crisis across cities and towns, leaving unprecedented numbers of people homeless and creating poor health conditions in precarious, concentrated homeless encampments. In Boston, Massachusetts, an October 2021 public health emergency declaration preceded a January 2022 massive relocation campaign that moved over 200 people from a large street encampment into 5 novel “harm reduction housing” (HRH) programs. The area is known for its proximity to area hospitals, its open-air drug market, and violence related to drugs and crime. These programs provide housing units with access to harm reduction supplies like sterile syringes and other safer use materials, naloxone, and low-barrier medication treatment, and staff provide these services according to policies that champion the principles of “meeting people where they are”. But the HRH sites differ in ways that may affect resident outcomes, and uptake of services vary. Data suggest that housing interventions may tragically increase isolation and thus overdose risk; others claim lives will be saved and life-saving treatments will start because of their improved access at the HRH sites. An initial case-crossover analysis of those recently relocated echoed a mixture of positive and negative effects. Lacking clear-cut, scientifically rigorous processes that consider both intended and unintended consequences of these actions, we propose a rapid, mixed methods study to efficiently examine the immediate effects of the relocation efforts and the longer-term impacts of living in the novel HRH. Specifically, this time-sensitive study will collect survey, interview, and drug supply data from the community of people who are homeless and use drugs in the concentrated area of Boston who have been affected by these recent actions. The study will help to determine short and long-term impacts of: a) rapid relocation and how residents successfully navigated it; and b) co-provision of harm reduction services and housing on individual- level behaviors and local drug supply outcomes. Specific aims are to: Aim 1) Develop a measure of harm reduction services and policies to inventory their provision and use in HRH sites for studying continuity, uptake, and evolution of care. Aim 2) Enroll an observational cohort following 100 HRH residents for 12 months to catalogue relocation effects and understand how harm reduction services use changes drug use, HIV and drug risk behaviors, treatment uptake, and the local drug supply. Data specific to new HRH resident cohort members will augment our prior case-crossover analysis of relocation impacts. Aim 3) Conduct repeat, longitudinal one-on-one interviews with 25 cohort members to gain greater insight into the nuances of relocation and HRH residence, including health and safety impacts, changes in collective efficacy, and gender considerations. Findings will contribute to harm reduction science and will be directly relevant to jurisdi...