More than a year after the enactment of the Paul Wellstone and Pete Domenici Mental Health Parity and Addiction Equity Act of 2008 (MHPAEA), the Departments of Labor, Health and Human Services, and Treasury issued interim final rules (IFR) prohibiting group health plans and insurance from applying more restrictions on mental health or substance use disorder benefits than they do for medical/surgical benefits. In the absence of formal guidance until the publication of the IFR and with the MHPAEA requiring compliance for plan years starting on or after October 3, 2009, many group health plans have been operating under a good-faith compliance standard. The IFR from the federal agencies provides significant guidance in some areas, and several of the requirements will necessitate additional steps to ensure compliance. Understanding how the IFR may affect the business of behavioral healthcare and the decisions that follow will be of great importance to all interested parties, including health insurance companies, health plans, employers, providers, and consumers of behavioral healthcare.