The Supreme Court in District of Columbia v. Heller held that the Second Amendment protects an individual's right to possess a firearm, unconnected to service in a militia, and protects the right to use that firearm for traditional lawful purposes such as self-defense within the home. The Court conducted an extensive analysis of the Second Amendment to interpret its meaning, but the decision left unanswered other significant constitutional questions, including the standard of scrutiny that should be applied to laws regulating the possession and use of firearms, and whether the Second Amendment applies to the states. Three federal appellate circuits have since addressed whether the Second Amendment applies to the states. Two of these circuits, the Second and Seventh, both held that the Second Amendment did not apply to the states, whereas the Ninth Circuit has initially held that the Second Amendment is applicable to the states, although a rehearing en banc is scheduled and may affect that decision. This report presents an overview of the principles of incorporation, the early Supreme Court cases that addressed the application of the Second Amendment to state governments, and the federal appellate cases that have addressed incorporation of the Second Amendment since the Heller decision.