Understanding how health care markets function is important not only because competition has a direct influence on the price and utilization of health care services, but also because the proper functioning, or lack thereof, of health care markets has a very real impact on patients who depend on health care markets and providers for their personal well-being. In this dissertation, I examine the role of government policies and regulation in health care markets, with a focus on the response of health care providers. In Chapter 1, I analyze the impact of Medicare payment rules on hospital ownership of physician practices. Since the mid-2000’s, there has been a rapid increase in hospital ownership of physician practices, however, there is little empirical research which addresses the causes of this recent wave of integration. Medicare’s “provider-based” billing policy allows hospital-owned physician practices to charge higher reimbursement rates for services provided compared to a freestanding, independent physician practice, without altering how or where services are provided. This “site-based” differential creates a premium for physicians to integrate with hospitals, and the size of this differential varies with the types of health care services provided. I find that Medicare payment rules have contributed to hospital ownership of physician practices and that the response varies across physician specialties. A 10 percent increase in the relative reimbursement rate paid to integrated physicians leads to a 1.9 percentage point increase in the probability of hospital ownership for Medical Care specialties, including cardiology, neurology, and dermatology, which explains about one-third of observed integration of these specialties from 2005 through 2015. Magnitudes for Surgical Care specialties are similar, but more sensitive across specifications. There is no significant response for Primary Care physicians. In combination with other empirical literature which finds that integration between physicians and hospitals typically results in higher prices with no impact on costs or quality of care, I cautiously interpret this responsiveness as evidence that Medicare’s provider-based billing policy overcompensates integrated physician practices and leads to an inefficiently high level of vertical integration between physician and hospitals. In Chapter 2, I analyze the effect of anti-fraud enforcement activity on Medicaid spending, with a particular focus on the False Claims Act. The False Claims Act (FCA) is a federal statute which protects the government from making undeserved payments to contractors and suppliers. Individual states have chosen to enact their own versions of the federal FCA, and these statutes have increasingly been used to target health care fraud. FCA statutes commonly include substantial monetary penalties such as “per-violation” monetary fines and tripled damages, as well as a “whistleblower” provision which allows private plaintiffs to initiate a lawsuit and collect a portion of recoveries as a reward. Using variation in statelevel FCA legislation, I find state FCAs reduce Medicaid prescription drug spending by 21 percent, while other spending categories - which are less lucrative for FCA lawsuits - are unresponsive. Within the prescription drug category, drugs prone to off-label use show larger declines in response to the whistleblower laws, consistent with FCA lawsuits being used to prosecute pharmaceutical manufacturers for off-label marketing and promotion. Spending and prescription volume for drugs prone to off-label use fall by up to 14 percent. This effect could be driven by pharmaceutical manufacturers’ changes in physician detailing for drugs prone to off-label use and/or physicians’ changes in prescribing behavior.