Behavioral health problems are highly prevalent among people with serious medical illness. Individuals living with these comorbidities have complex clinical and social needs yet face siloed care, high health care costs, and poor outcomes. Interacting factors contribute to these inequalities including historical separation of behavioral and physical health provision. Several care models for integrating behavioral health and general medical care have been developed and tested, but the evidence base focuses primarily on primary care populations and settings. This article advances that work by proposing a Behavioral Health-Serious Illness Care model. Developed through a mixed methods approach combining literature review, surveys, interviews, and input from an expert advisory panel, it provides a conceptual framework of building blocks for behavioral health integration tailored to serious illness care populations and the range of settings in which they receive care. The model is intended to serve as foundation to support the development and implementation of integrated behavioral health and serious illness care. The key components of the model are described, barriers to implementation discussed, and recommendations for policy approaches to address these barriers presented.