In United States constitutional theory, compact theory is an interpretation of the Constitution which asserts the United States was formed through a compact agreed upon by all the states, and that the federal government is thus a creation of the states. Consequently, under the theory, states are the final arbiters over whether the federal government has overstepped the limits of its authority as set forth in the compact. Compact theory contrasts with contract theory, which holds that the United States was formed with the consent of the people—rather than the consent of the states—and thus the federal government has supreme jurisdiction over the states. Compact theory has never been upheld by the courts.

Compact theory featured heavily in arguments by southern political leaders in the run up to the American Civil War that states had a right to nullify federal law and to secede from the union. It also featured in southern arguments opposing desegregation after the 1954 Supreme Court decision in Brown v. Board of Education. The theory also entered into the Mexico–United States border crisis of the early 2020s.

Supreme Court rulings The U.S. Supreme Court has rejected the idea that the Constitution is a compact among the states. Rather, the Court has stated that the Constitution was established directly by the people of the United States, not by the states. In one of the Supreme Court's first significant decisions, Chisholm v. Georgia (1793), Chief Justice John Jay stated that the Constitution was established directly by the people. Jay noted the language of the Preamble of the Constitution, which states that the Constitution was ordained and established by "We the people," and he stated: "Here we see the people acting as sovereigns of the whole country, and, in the language of sovereignty, establishing a Constitution by which it was their will that the State governments should be bound.""[The people] made a Confederation of the States the basis of a general government [i.e. the Articles of Confederation]. Experience disappointed the expectations they had formed from it, and then the people, in their collective and national capacity, established the present Constitution. It is remarkable that, in establishing it, the people exercised their own rights, and their own proper sovereignty, and, conscious of the plenitude of it, they declared with becoming dignity, 'We the people of the United States, do ordain and establish this Constitution.' Here we see the people acting as sovereigns of the whole country, and, in the language of sovereignty, establishing a Constitution by which it was their will that the State governments should be bound, and to which the State Constitutions should be made to conform. Every State Constitution is a compact made by and between the citizens of a State to govern themselves in a certain manner, and the Constitution of the United States is likewise a compact made by the people of the United States to govern themselves as to general objects in a certain manner." Chisholm v. Georgia, 2 U.S. (2 Dall.) 419 (1793). Jay went on to say that the people had delegated to the federal judiciary the task of interpreting the meaning, construction, and operation of the Constitution.

This view has been repeatedly affirmed by the Court. In Martin v. Hunter's Lessee (1816), the Supreme Court explicitly rejected the idea that the Constitution is a compact among the states: "The Constitution of the United States was ordained and established not by the States in their sovereign capacities, but emphatically, as the preamble of the Constitution declares, by 'the people of the United States.'" The Court contrasted the earlier Articles of Confederation with the Constitution, characterized the Articles of Confederation as a compact among states, and stated that the Constitution was established by not the states but the people."The Constitution of the United States was ordained and established not by the States in their sovereign capacities, but emphatically, as the preamble of the Constitution declares, by 'the people of the United States.'... The Constitution was for a new Government, organized with new substantive powers, and not a mere supplementary charter to a Government already existing. The Confederation was a compact between States, and its structure and powers were wholly unlike those of the National Government. The Constitution was an act of the people of the United States to supersede the Confederation, and not to be ingrafted on it, as a stock through which it was to receive life and nourishment." Martin v. Hunter's Lessee, 14 U.S. (1 Wheat.) 304 (1816). Likewise, in McCulloch v. Maryland (1819), the Supreme Court stated that the federal Constitution proceeded directly from the people and was not created by the states. It stated that the Constitution was binding on and could not be negated by the states. It again contrasted the Articles of Confederation, which was established by the states, to the Constitution, which was established by the people."The government proceeds directly from the people; is 'ordained and established' in the name of the people, and is declared to be ordained, 'in order to form a more perfect union, establish justice, insure domestic tranquillity, and secure the blessings of liberty to themselves and to their posterity.'... It required not the affirmance, and could not be negatived, by the State Governments. The Constitution, when thus adopted, was of complete obligation, and bound the State sovereignties.... To the formation of a league such as was the Confederation, the State sovereignties were certainly competent. But when, 'in order to form a more perfect union,' it was deemed necessary to change this alliance into an effective Government, possessing great and sovereign powers and acting directly on the people, the necessity of referring it to the people, and of deriving its powers directly from them, was felt and acknowledged by all. The Government of the Union then (whatever may be the influence of this fact on the case) is, emphatically and truly, a Government of the people. In form and in substance, it emanates from them. Its powers are granted by them, and are to be exercised directly on them, and for their benefit." McCulloch v. Maryland, 17 U.S. (4 Wheat.) 316 (1819). After the Civil War, in Texas v. White (1869), a case discussing the legal status of the southern states that had attempted to secede, the Supreme Court stated that the union was not merely a compact among states but was "something more than a compact.""When, therefore, Texas became one of the United States, she entered into an indissoluble relation. All the obligations of perpetual union, and all the guaranties of republican government in the Union, attached at once to the State. The act which consummated her admission into the Union was something more than a compact; it was the incorporation of a new member into the political body. And it was final. The union between Texas and the other States was as complete, as perpetual, and as indissoluble as the union between the original States." Texas v. White, 74 U.S. (7 Wall.) 700 (1869).

Arguments in favor Leading proponents of this view of the U.S. Constitution primarily originated from Virginia and other southern states. Notable proponents of the theory include Thomas Jefferson.Jefferson to William B. Giles in letter dated 12/26/1825. Under this theory and in reaction to the Alien and Sedition Acts of 1798, Jefferson claimed the federal government overstepped its authority, and advocated nullification of the laws by the states. The first resolution of the Kentucky Resolutions began by stating: Resolved, that the several States composing the United States of America, are not united on the principles of unlimited submission to their General Government; but that by compact under the style and title of a Constitution for the United States and of amendments thereto, they constituted a General Government for special purposes, delegated to that Government certain definite powers, reserving each State to itself, the residuary mass of right to their own self Government; and that whensoever the General Government assumes undelegated powers, its acts are unauthoritative, void, and of no force; that to this compact each state acceded as a state, and is an integral party; that the Government created by this compact was not made the exclusive or final judge of the extent of the powers delegated to itself; since that would have made its discretion, and not the Constitution, the measure of its powers; but that, as in all other cases of compact among powers having no common judge, each party has an equal right to judge for itself, as well of infractions as of the mode and measure of redress.Kentucky Resolutions of 1798; see also "Reclaiming the American Revolution," Wm. J. Watkins, Jr., Palgrave MacMillan, 2008, p.165.

Meanwhile, James Madison had asserted in Federalist No. 39 that "the people" were "not as individuals composing one entire nation, but as composing the distinct and independent States to which they respectively belong"; the Constitution was "to be the assent and ratification of the several States, derived from the supreme authority in each State, the authority of the people themselves"; and "the act of the people, as forming so many independent States, not as forming one aggregate nation, is obvious from this single consideration." Likewise, as noted in Article VII of the Constitution, ratification took place not by a single popular convention but conventions of only the ratifying states and would carry the Constitution into effect only between those ratifying states.

Arguments against Others have taken the position that the federal government is not a compact among the states but was instead formed directly by the people in their exercise of their sovereign power. The people determined that the federal government should be superior to the states. Under this view, the states are not parties to the Constitution and do not have the right to determine for themselves the proper scope of federal authority but instead are bound by the determinations of the federal government. The state of Vermont took that position in response to the Kentucky Resolutions.In response to the Kentucky Resolutions' assertion that the states formed the federal government by compact and retained the right to judge the federal government's laws, Vermont stated, "This cannot be true. The old confederation, it is true, was formed by the state Legislatures, but the present Constitution of the United States was derived from a higher authority. The people of the United States formed the federal constitution, and not the states, or their Legislatures. And although each state is authorized to propose amendments, yet there is a wide difference between proposing amendments to the constitution, and assuming, or inviting, a power to dictate and control the General Government." Daniel Webster advocated that view in his debate with Robert Hayne in the Senate in 1830: