Article IV · Section 1 of 4
States respect each other's records
Article IV: The states
The one-line version
States must accept each other's laws, records, and court rulings.
Section 1 in plain English
Each state must give "Full Faith and Credit" to the laws, records, and court rulings of every other state. This means a state must generally accept them as valid. Congress can pass laws about how these records are proved and what effect they have.
Original text, 1788
Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State. And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.