Medicaid is the largest single source of health insurance coverage in the United States, providing insurance for more than 62 million persons and families in 2013. The Patient Protection and Affordable Care Act sought to expand Medicaid eligibility to nearly all low-income persons with incomes up to 138% of the federal poverty level. However, the U.S. Supreme Court ruled that states' expansion would be optional. Although more than half of the states and the District of Columbia have opted to expand Medicaid starting in 2014, many states continue to oppose increasing access to the program. This article will discuss the basic provisions of the expansion and the benefits and challenges patients and physicians may face as Medicaid grows.