Bill of Rights / The Constitution

We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

The Tenth Amendment.
http://www.billofrights.com/tenth_amendment.htm

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved for the States respectively, or to the people.

� The Tenth Amendment, which makes explicit the idea that the federal government is limited only to the powers it is granted in the Constitution, is generally recognized to be a truism. In United States v. Sprague (1931) the Supreme Court noted that the amendment "added nothing to the [Constitution] as originally ratified." From time to time states and local governments have attempted to assert exemption from various federal regulations, especially in the areas of labor and environmental controls, using the Tenth Amendment as a basis for their claim.

Another often-repeated quote, from United States v. Darby, 312 U.S. 100, 124 (1941), states: The amendment states but a truism that all is retained which has not been surrendered. There is nothing in the history of its adoption to suggest that it was more than declaratory of the relationship between the national and state governments as it had been established by the Constitution before the amendment or that its purpose was other than to allay fears that the new national government might seek to exercise powers not granted, and that the states might not be able to exercise fully their reserved powers.

Source: Wikipedia