Primary care physician (PCP) shortages have been a barrier to accessing care for millions of Americans, particularly those living in areas facing the worst shortages - primary care health professional shortage areas (HPSAs). Increased use of nurse practitioners (NPs) has been proposed as a solution to the shortages as NPs can effectively substitute for PCPs. However, this proposal has been hampered by regulatory restrictions on NP scope-of-practice (SOP) that exist in many states. While some states permit NPs to practice and prescribe medications independent of physicians (NP independence), others require extensive physician supervision that limit NPs ability to provide care and substitute for PCPs. Despite the limitations that restrictive regulations pose to improving access to primary care, research evidence of their effect on access in primary care HPSAs is limited. This dissertation fills this gap in the literature. Using individual-level data from the Medical Expenditure Panel Surveys (1996-2015) and a difference-in-differences approach, I exploit variation in NP independence across states and over time to evaluate the impact of NP independence on access to primary care in HPSAs Further, I examined for heterogeneity in the effect of NP independence between HPSAs and non-HPSAs as well as effect heterogeneity in HPSAs based on individual (age, insurance status, and insurance type) and health system characteristics (availability of primary care facilities and NP Medicaid reimbursement rate) I find that NP independence led to a 5% increase in the number of individuals with a primary care provider and a 2% increase in the use of non-physicians (relative to physicians) as the primary care provider in HPSAs. However, non-HPSAs experienced no significant changes in access to care. Further, I find evidence of heterogeneity in the effect of NP independence in HPSAs for all three individual characteristics but find no significant effect heterogeneity for any of the health system characteristics. Non-elderly individuals experienced greater improvements in access following NP independence compared to their elderly counterparts, and while both insured and uninsured individuals experienced improvements in access to care, uninsured individuals benefitted more from NP independence. Further, I find evidence of greater improvements in access to care among Medicaid beneficiaries relative to their privately insured and Medicare counterparts. These findings imply that removing regulatory restrictions on NP SOP could be an effective policy strategy for mitigating the effects of PCP shortages and improving access to care in HPSAs. Further, they demonstrate that NP independence could be a viable tool for addressing access to care issues in two traditionally underserved populations – the uninsured and Medicaid beneficiaries. Beyond addressing access issues, NP independence could also mitigate rising health care costs. The finding of increased use of lower-cost non-physicians rather than their more costly physician counterparts after NP independence indicates that this policy change could also bring about cost savings for society.