PROJECT SUMMARY ABSTRACT Improving access to surgical care remains a persistent challenge in the United States. While some areas of the country are crowded with high-intensity resources, more than a third of US counties do not have a single surgeon. Even in areas where there are enough providers, more than 29 million American lack insurance coverage preventing access to elective surgical care. As a result of a limited surgical workforce, inadequate insurance coverage or both, patients with limited access delay care until the condition requires emergent intervention. These emergency operations, that are more costly than their elective counterparts due to more complication and readmissions, are estimated to account for more than $1 billion in preventable spending. In response, the Centers for Medicare and Medicaid Services (CMS) implemented multiple access strategies including broader insurance coverage (e.g. Medicaid Expansion) and workforce incentives (e.g. Health Profession Shortage Areas (HPSA)). By improving access, the policies are meant to facilitate elective surgical care, prevent adverse events and reduce episode spending. Because the CMS policies outlined here focus on improving access, we will evaluate a broad range access sensitive surgical conditions. These conditions are preferentially treated with elective, or scheduled, operations when access is optimal. However, when access is limited, their natural progression leads to unresolving symptoms that ultimately require an emergency surgical procedure. Examples include abdominal aortic aneurysms which can rupture, ventral hernias which can strangulate, and colorectal cancers that can cause life-threatening obstructions. As such, these operations being performed electively versus emergently can serve as an indicator of access. Each CMS policy was implemented with both geographic and temporal variation resulting in beneficiaries exposed to one policy, both policies or neither. We will exploit these overlapping natural experiments to understand and isolate the effects of each policy alone as well as their combined effects using administrative claims from Medicare Claims and Healthcare Costs Utilization Project. We will leverage our extensive experience with natural experiment study design to appropriately isolate the effects of each policy on surgical access, quality and costs. This study will bring important evidence to evidence-based policy making as many states are still adopting Medicaid Expansion and congress debates the merits of continued HPSA subsidies.