Purpose: This study sought to describe features of the physical space in which practices integrating primary care and behavioral health care work and to identify the arrangements that enable integration of care.Methods: We conducted an observational study of 19 diverse practices located across the United States. Practice-level data included field notes from 2-4-day site visits, transcripts from semistructured interviews with clinicians and clinical staff, online implementation diary posts, and facility photographs. A multidisciplinary team used a 4-stage, systematic approach to analyze data and identify how physical layout enabled the work of integrated care teams.Results: Two dominant spatial layouts emerged across practices: type-1 layouts were characterized by having primary care clinicians (PCCs) and behavioral health clinicians (BHCs) located in separate work areas, and type-2 layouts had BHCs and PCCs sharing work space. We describe these layouts and the influence they have on situational awareness, interprofessional "bumpability," and opportunities for on-the-fly communication. We observed BHCs and PCCs engaging in more face-to-face methods for coordinating integrated care for patients in type 2 layouts (41.5% of observed encounters vs 11.7%; P < .05). We show that practices needed to strike a balance between professional proximity and private work areas to accomplish job tasks. Private workspace was needed for focused work, to see patients, and for consults between clinicians and clinical staff. We describe the ways practices modified and built new space and provide 2 recommended layouts for practices integrating care based on study findings. Layout of physical space affects how professionals work together across diverse settings. [1][2][3][4] In health care, design of the physical environment has been associated with health-care quality, work efficiency, and cost effectiveness. 5,6 However, most research on evidence-based health design has focused on This article was externally peer reviewed. Conclusion