The Patient Protection and Affordable Care Act (ACA) will expand coverage of mental health and substance use disorder benefits and federal parity protections to over 60 million Americans. The key to this expansion is the essential health benefit provision in the ACA that requires coverage of mental health and substance use disorder services at parity with general medical benefits. Other ACA provisions that should improve access to treatment include requirements on network adequacy, dependent coverage up to age 26, preventive services, and prohibitions on annual and lifetime limits and preexisting exclusions. The ACA offers states flexibility in expanding Medicaid (primarily to childless adults, not generally eligible previously) to cover supportive services needed by those with significant behavioral health conditions in addition to basic benefits at parity. Through these various new requirements, the ACA in conjunction with Mental Health Parity and Addiction Equity Act (MHPAEA) will expand coverage of behavioral health care by historic proportions.