Interprofessional collaboration is crucial to reduce overincarceration of people with severe mental illness. Learning how to collaborate occurs in 2 complementary ways. One model emphasizes cognitive tasks: becoming familiar with the values and knowledge of other disciplines. Another model emphasizes practical interactive skills: calibrating one's preexisting expertise to the demands of the local workplace. This qualitative study assesses the 2 models in the case of psychiatrists in a multidisciplinary mental health court who learned to divert people with psychiatric disease from jail and hence advance the court's mission. Ethnographic research was conducted over 4 years with the staff of a US mental health court. Interviews with 3 psychiatrists and observations of 87 staff meetings and probation review hearings were recorded on handwritten notes. Notes were transcribed, entered into a qualitative database management program (NVivo 12), and coded using the grounded theory approach. A master codebook was developed to identify crosscutting themes. Psychiatrists did not need deep familiarity with the values or skills of legal professionals to divert people with psychiatric disease from incarceration. They successfully inserted their expertise through 3 strategies-teaching about pharmaceutics, suggesting concrete interventions based on details of diagnosis and behavior, and shifting the collective assessment of defendants from a punitive to a therapeutic framework-that depended on their acquiring new interactive skills. However, they failed in their efforts to refine the eligibility criteria for admitting new defendants to the court; their expertise was underutilized because of the makeup of this interprofessional team. Reducing the overincarceration of people with severe mental illness depends on interprofessional collaboration. This study shows that discerning opportunities for (and blockages to) applying one's preexisting expertise and learning the perspective of other disciplines are key complementary ingredients of interprofessional learning in this setting. Research in other treatment courts is needed to assess the generalizability of this single case study.