Background: There is a lack of research on psychotherapy interventions for transition-aged students ages 18 to 21 that integrate horses or other equines in the provision of services. A critical early task in researching such complex interventions involves elucidating an intervention's critical elements and theoretical assumptions. Purpose: The purpose of this study was to develop a theory-driven logic model of a psychotherapy program for transition-aged students ages 18 to 21 that incorporated horses. Methodology/Approach: The research approach was qualitative description, a low-inference form of qualitative research. Data were collected via interviews with program stakeholders and through review of program documents, and were analyzed using a directed content analysis. Findings/Conclusions: The resulting logic model elucidates theoretical assumptions, activities, resources, outputs, outcomes, and theorized community impact of the psychotherapy program integrating horses. Implications: This study addresses several gaps in existing research on equine-assisted services, particularly the need to thoroughly describe an intervention and its theoretical assumptions, which can guide future program refinement and replication, and future research.