A trier of fact, or finder of fact, is a person, or group of persons, who determines facts in a legal proceeding, usually a trial. To determine a fact is to decide, from the evidence, whether something existed or some event occurred. Various aspects of a case that are not in controversy may be the "facts of the case" and are determined by the agreement of the separate parties; the trier of fact need not decide such issues.
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 amounts to jury nullification, e.g. the jury effectively re-writing the law or blatantly ignoring it in a particular case.
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."
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.