The equal footing doctrine, also known as equality of the states, is the principle in United States constitutional law that all states admitted to the Union under the Constitution since 1789 enter on equal footing with the 13 states already in the Union at that time. The Constitution grants to Congress the power to admit new states in Article IV, Section 3, Clause 1, which states:
New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
In each act of admission since that of Tennessee in 1796, Congress has specified that the new state joins the Union "on an equal footing with the original States in all respects whatever". Previously, when Vermont was admitted in 1791, its act of admission said Vermont was to be "a new and entire member" of the United States.