Burden of proof is a legal duty that encompasses two connected but separate ideas that apply for establishing the truth of facts in a trial before tribunals in the United States: the "burden of production" and the "burden of persuasion." In a legal dispute, one party is initially presumed to be correct, while the other side bears the burden of producing evidence persuasive enough to establish the truth of facts needed to satisfy all the required legal elements of legal dispute. There are varying types of burden of persuasion commonly referred to as standards of proof, and depending on the type of case, the standard of proof will be higher or lower. Burdens of persuasion and production may be of different standards for each party, in different phases of litigation. The burden of production is a minimal burden to produce at least enough evidence for the trier of fact to consider a disputed claim. After litigants have met the burden of production, they have the burden of persuasion: that enough evidence has been presented to persuade the trier of fact that their side is correct. There are different standards of persuasiveness ranging from a preponderance of the evidence, where there is just enough evidence to tip the balance, to proof beyond a reasonable doubt, as in United States criminal courts.

The burden of proof is always on the person who brings a claim in a dispute. It is often associated with the Latin maxim semper necessitas probandi incumbit ei qui agit, a translation of which in this context is: "the necessity of proof always lies with the person who lays charges." In civil suits for example, the Plaintiff bears the burden of proof that the Defendant's action or inaction caused injury to the Plaintiff, and the Defendant bears the burden of proving an affirmative defense.

The party that does not carry the burden of proof is presumed to be correct, until the burden shifts after the party with the burden of proof meets its burden. An example is in an American criminal case, where there is a presumption of innocence by the defendant. Once a party meets its burden of proof, the burden then shifts to the other party.

However in English law, there is no such presumption. In England, if the claimant fails to discharge the burden of proof to prove their case, the claim will be dismissed: the defendant will not have a case to answer. If however the claimant does adduce some evidence and discharges the burden of proof so as to prove its own case, it is for the defendant to adduce evidence to counter that evidence of proof of the alleged facts. If after weighing the evidence in respect of any particular allegation of fact, the court decides whether the (1) the claimant has proved the fact, (2) the defendant has proved the fact, or (3) neither party has proved the fact. Thus the concept of burden of proof works differently in different countries: ie under different systems of law.