The Institute of Medicine, in its 2001 Crossing the Quality Chasm report, recommended greater integration and coordination as a component of a transformed health care system, yet relationships between acute and post-acute providers have remained weak. With payment reforms that hold hospitals and health systems accountable for the total costs of care and readmissions, the dynamic between acute and post-acute providers is changing. In this article, we outline the internal and market factors that will drive health systems' decisions about whether and how they integrate with post-acute providers. Enhanced integration between acute and post-acute providers should reduce variation in post-acute spending.