The Full Faith and Credit Clause is a clause in the Constitution of the United States which states that “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.” Put in simple language, this means that judgments rendered in one state are acknowledged in others.
When the Constitution was drafted, Article IV, Section 1 was included to protect the autonomy of the states while also promoting unity in the United States as a whole. The framers wanted to make sure that judicial proceedings in one state would be respected by all states, because otherwise there could be substantial room for abuse. This affirmed the autonomy of the individual states, an important concern for many of the people involved in the drafting of the Constitution, while ensuring that the states would also be unified.
In a very simple example of why the Full Faith and Credit Clause is important, consider the case of a couple divorcing in Arkansas. Without the clause, that divorce would not be recognized outside of the state. If one of the partners moved to Vermont, it would be necessary to file all over again, otherwise that partner would still be considered married. With the clause the State of Vermont recognizes the divorce filed and approved in the State of Arkansas.
This clause in the Constitution also prevents abusive litigation. If someone in Texas sues someone and the court delivers a valid judgment, this person cannot file the same suit in Kansas — the outcome of the suit in Texas is recognized and considered to be the final judgment. Likewise, someone who is ruled against in litigation in Colorado cannot flee to New York and evade punishment, because the ruling in the Colorado court is still valid in New York.
The Full Faith and Credit Clause also plays a role in reciprocity. Professionals such as doctors and lawyers are not required to go to school all over again when they move to new states; they can apply for reciprocity in certification so that they can practice. Likewise, when citizens move to new states, they can renew their driving licenses in the new state without having to go through drivers' education a second time. As long as the standards for licensure are similar between the two states, no additional training or certification will be required for reciprocity.