The Militia Act of 1903, also known as the Efficiency in Militia Act of 1903 or the Dick Act, was legislation enacted by the United States Congress to create what would become the modern National Guard from a subset of the militia, and codify the circumstances under which the Guard could be federalized. It also provided federal funds to pay for equipment and training, including annual summer encampments. The new National Guard was to organize units of similar form and quality to those of the regular Army, and intended to achieve the same training, education, and readiness requirements as active duty units.

The National Guard is a state-based military force that becomes part of the U.S. military's reserve components of the U.S. Army and the U.S. Air Force when activated for federal missions. It is a military reserve force composed of National Guard military members or units of each state and the territories of Guam, the Virgin Islands, Puerto Rico, and the District of Columbia, for a total of 54 separate organizations. It is officially created under Congress's Article 1 Section 8 ability to "raise and support armies". All members of the National Guard are also members of the organized militia of the United States as defined by 10 U.S.C. § 246. National Guard units are under the dual control of state governments and the federal government.