Project Summary Currently, 2.2 million individuals are incarcerated in the United States (US), and approximately 600,000 are released annually. Substance use disorders (SUDs) are common in this population: ~65% meet the criteria for an SUD diagnosis (vs 5% of the general population). Post- incarceration, substance use increases considerably, – the risk of drug overdose is 9-17 times higher among formerly incarcerated individuals than in the general population. However, significant gaps in our understanding of structural and individual pathways of post-incarceration substance use limit treatment effectiveness. The proposed study will examine factors associated with changes in substance use and substance use treatment adequacy over a one- year period post-release among formerly incarcerated individuals in New York City (NYC), where opioid-related overdose rates more than doubled between 2015 and 2017 and are increasing among people of color and residents in high poverty communities. We will examine the extent to which participants receive substance use treatment services recommended by their scores on the American Society of Addiction Medicine (ASAM) patient placement criteria (PPC). We will use novel spatially informed multi-level modeling strategies to investigate individual and environmental factors that influence substance use among individuals released in NYC from institutions in the New York State Department of Corrections and Community Supervision (NYSDOCCS), one of the largest U.S. criminal justice correctional agencies. Guided by social ecological theory, we will address the following Specific Aims: 1). Characterize substance use at five time points over a 12-month period (at baseline and 3-, 6-, 9-, and 12- months) among those recently released from incarceration; 2). Identify individual- and environment-level predictors of post-incarceration substance use; and 3) Investigate discrepancies between ASAM PPC composite scores (a measure of addiction severity) generated and levels of substance use treatment over time. The proposed research will identify substance use treatment gaps and influential factors that are amenable to intervention in the interest of informing effective responses to problematic substance use.