The 2010 Patient Protection and Affordable Care Act (ACA) requires not-for-profit hospitals, including Catholic hospitals, to engage in meaningful community assessment and collaboration efforts in order to maintain their tax-exempt status. Now that the ACA has been upheld by the U.S. Supreme Court, this paper argues that the requirements related to a more robust community engagement process should be embraced by Catholic not-for-profit hospitals and health systems. Apart from the legal requirements under ACA, an equally persuasive moral mandate to engage in community-level assessment and action exists in the ethical tradition of Catholic health care, particularly in the notions of the common good, preferential option for the poor, and subsidiarity. This paper examines the compelling nature of these moral norms in light of the dual goals of improving overall community health and reducing health disparities among vulnerable populations. It concludes with the examination of one model of community collaboration: Mobilizing for Action through Planning and Partnerships (MAPP).