Underinsurance is most commonly defined as the state in which people with medical coverage are still exposed to financial risk. We argue that the adequacy of health insurance coverage should also be assessed in terms of the adequacy of specific benefits coverage and access to care. Underinsurance can be understood conceptually as comprising three separate domains: (a) the economic features of health insurance, (b) the benefits covered, and (c) access to health services. The literature provides ample evidence that people who are underinsured have high financial risk and face barriers in access to care similar to those who are completely uninsured. In response to the growing recognition of the problems associated with underinsurance, the Patient Protection and Affordable Care Act of 2010 includes numerous provisions designed to limit costs to consumers, to assure a minimum set of benefits, and to enhance access to care, especially primary care.