As a result of large-scale changes in insurance coverage under the Affordable Care Act (ACA), financing streams for safety net providers will shift. The law provides significant resources for further development of some safety net providers while reducing funding streams for others. The vulnerable populations served by the safety net—poor and underserved communities—may not fundamentally change, but their sources of coverage, and thus, financing for safety net providers who care for these populations, will shift dramatically. To adapt to these changing funding streams, safety net providers will need to engage in new and ongoing payment reform efforts, negotiate their roles with state Medicaid programs and qualified health plans sold through newly established insurance exchanges, and maintain an infrastructure to serve the remaining uninsured. This report, the third in a series that reflects the work of the National Workgroup on integrating a Safety Net into Health Care Reform Implementation, addresses the workforce and financing infrastructure needed to support a sustainable safety net to serve vulnerable populations.