The Mental Health Parity and Addiction Equity Act (MHPAEA) of 2008 changed the landscape of mental health and substance use disorder coverage in the United States. The MHPAEA's comprehensiveness compared with past parity laws, including its extension of parity to plan management strategies, the so-called nonquantitative treatment limitations (NQTL), led to significant improvements in mental health care coverage. In this article, we review the history of this landmark legislation and its recent expansions to new populations, describe past research on the effects of this and other mental health/substance use disorder parity laws, and describe some directions for future research, including NQTL compliance issues, effects of parity on individuals with severe mental illness, and measurement of benefits other than mental health care use. Expected final online publication date for the Annual Review of Public Health Volume 39 is April 1, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.