The Patient Protection and Affordable Care Act will expand insurance coverage to millions of Americans with mental disorders. One particularly important implementation issue is the scope of mental health and substance abuse services under expanded health insurance coverage. This article examines current public and commercial insurance coverage of the range of services used by individuals with mental illnesses and substance use disorders and assesses the implications of newly mandated standards for benefit packages offered by public and private plans. The authors note that many services needed by individuals with mental or substance use disorders fall outside the scope of benefits currently covered by a typical private insurance plan. Compared with other insurers, Medicaid currently covers a broader range of behavioral health services; however, individuals moving into Medicaid under new eligibility pathways will receive "benchmark" or "benchmark-equivalent" coverage rather than full Medicaid benefits. If behavioral health benefits are set at those currently available in typical private plans or in benchmark coverage, some newly insured individuals with mental illnesses or substance use disorders who are covered by private plans or Medicaid expansions are still likely to face gaps in covered services. Policy makers have several options for addressing these likely gaps in coverage, including requiring states to maintain coverage of some support services, including certain behavioral health services in the "essential benefits package," and expanding eligibility for full Medicaid benefits.