On April 16, 2015 the Mercury and Air Toxics Standards (MATS) rule went into effect. While a significant number of coal-fired electric generating units (EGUs) will achieve compliance using controls installed to meet regulations that pre-date MATS, many units plan to upgrade existing controls, install additional controls, or retire. A large number of coal-fired units have requested compliance extensions to finalize these compliance strategies. Over 154 gigawatts (GWs) of coal capacity have applied for MATS compliance extensions thus far, providing details on the wide variety of compliance strategies being implemented by individual units. This article provides an overview of MATS requirements, compliance options, and compliance extensions.