PURPOSE: To identify how organizations prepare clinicians to work together to integrate behavioral health and primary care. METHODS: Observational cross-case comparison study of 19 U.S. practices, 11 participating in Advancing Care Together, and 8 from the Integration Workforce Study. Practices varied in size, ownership, geographic location, and experience delivering integrated care. Multidisciplinary teams collected data (field notes from direct practice observations, semistructured interviews, and online diaries as reported by practice leaders) and then analyzed the data using a grounded theory approach. RESULTS: Organizations had difficulty finding clinicians possessing the skills and experience necessary for working in an integrated practice. Practices newer to integration underestimated the time and resources needed to train and organizationally socialize (onboard) new clinicians. Through trial and error, practices learned that clinicians needed relevant training to work effectively as integrated care teams. Training efforts exclusively targeting behavioral health clinicians (BHCs) and new employees were incomplete if primary care clinicians (PCCs) and others in the practice also lacked experience working with BHCs and delivering integrated care. Organizations' methods for addressing employees' need for additional preparation included hiring a consultant to provide training, sending employees to external training programs, hosting residency or practicum training programs, or creating their own internal training program. Onboarding new employees through the development of training manuals; extensive shadowing processes; and protecting time for ongoing education, mentoring, and support opportunities for new and established clinicians and staff were featured in these internal training programs. CONCLUSION: Insufficient training capacity and practical experience opportunities continue to be major barriers to supplying the workforce needed for effective behavioral health and primary care integration. Until the training capacity grows to meet the demand, practices must put forth considerable effort and resources to train their own employees.