A trier of fact or finder of fact is a person or group who determines which facts are available in a legal proceeding (usually a trial) and how relevant they are to deciding its outcome. To determine a fact is to decide, from the evidence presented, whether something existed or some event occurred.
The fact finder differs by the type of proceeding. In a jury trial, it is the jury. In a non-jury trial, the judge is both the fact finder and the trier of law. In administrative proceedings, the fact finder may be a hearing officer or a hearing body.
In a jury trial, a jury is the trier of fact. The jury finds the facts and applies them to the relevant statute or law it is instructed by the judge to use in order to reach its verdict. Thus, in a jury trial, the findings of fact are made by the jury while the judge makes legal rulings as to what evidence will be heard by the jury and what legal framework governs the case. Jurors are instructed to strictly follow the law as given by the judge, but are in no way obligated to do so. In some cases this leads to jury nullification, where the jury's verdict differs from what the law states.
In Anglo-American–based legal systems, finding of fact made by the jury is not appealable unless clearly wrong to any reasonable person. This principle is enshrined in the Seventh Amendment to the United States Constitution, which provides that "no fact tried by a jury, shall be otherwise re-examined in any Court of the United States, than according to the rules of the common law".
In a bench trial, judges are professional triers of fact. In a bench trial, the judge makes both findings of fact and rulings of law. The findings of a judge of first instance are not normally disturbed by an appellate court.
In the United States, an administrative law judge (ALJ) both presides over trials (and makes rulings of law) and adjudicates the claims or disputes (in other words, ALJ-controlled proceedings are bench trials) involving administrative law, but ALJs are not part of an independent judiciary.