For the past few decades, the United States has not produced enough primary care physicians. Moreover, too few physicians practice in rural and medically underserved areas, and the number of people lacking adequate access to primary care has increased. Meanwhile, studies have piled up pointing to the high quality of care that nurse practitioners (NPs) provide, and increasing numbers of policy-influencing bodies have recommended expanding the use of NPs in primary care. Yet, barriers to the expanded use of NPs persist, and, consequently, tens of millions of Americans lack adequate access to primary care services. This report describes and integrates new evidence from a research program focused on the primary care workforce, NPs’ role in primary care, and the potential for NPs to help solve the problem of Americans’ access to quality primary care.