The characteristics of the setting in which services are delivered often influence the implementation and practice of evidence-based programs (EBPs). In order to accommodate complex cases in diverse settings, community-based EBPs tend not to have standardized practice instructions. However, variation in practice of EBPs may have significant implications for program fidelity and outcomes. This study identifies service-setting factors associated with variation in practice of Critical Time Intervention (CTI). CTI is an empirically supported community-based psychiatric rehabilitation program designed to reduce homelessness among people with mental illness. Interview data were obtained from 12 CTI practitioners: 3 practitioners using CTI in a clinical trial, and 9 practitioners using CTI in 4 community-based agencies. The data are analyzed using dimensional analysis to contrast the first-hand CTI practice experiences of these practitioners. The results show service structure (e.g., platform for relationship building, staff to manage housing applications, and organizational policy on substance abuse) and agency services (e.g., existing resources and modalities) greatly influence practitioners’ operationalization of shared CTI goals and fundamental practice strategies. Findings inform additional CTI fidelity elements and important assessment of service settings for CTI implementation. The study highlights the crucial role of practitioners in EBP implementation and the importance of seeking practitioners’ feedback on their experiences with EBPs for ultimately improving the implementation of EBPs.