Conflict of Laws
Choice of law
Traditional vested-rights analysis applies the law of the place of injury. Modern approaches are interest analysis, the most significant relationship test (Restatement §6), and better law. Courts weigh contacts, policies, and party expectations. Characterization - tort, contract, property, or procedure - determines which rule applies. Renvoi may be accepted or rejected; the forum generally applies its own procedural rules.
Federal courts
A federal court in diversity follows the choice-of-law rules of the state in which it sits (Klaxon) and applies state substantive law (Erie). Statutes of limitations are usually substantive; tolling and burden rules vary.
Judgments
Full faith and credit requires recognition of a final judgment on the merits rendered by a court with jurisdiction, subject to limited defenses such as lack of jurisdiction or fraud. Penal and tax judgments are not enforced.
Domicile
Domicile requires physical presence plus intent to remain indefinitely; a person retains the prior domicile until a new one is established. Domicile governs divorce jurisdiction, taxation, and probate.
Marriage and family
Validity is generally determined by the law of the place of celebration; a strong public policy exception applies, notably for polygamy and close consanguinity.
Worked example
A couple validly marries in State A and moves to State B, which would not permit such a marriage. Under the place-of-celebration rule, State B generally recognizes the marriage unless its public policy exception is clearly triggered.
Rule of thumb: characterize the issue and the states' contacts first; then select the approach.