Appellate jurisdiction  Appellate jurisdiction is the power of an appellate court to review, amend and overrule decisions of a trial court or other lower tribunal. Most appellate jurisdiction is legislatively created, and may consist of appeals by leave of the appellate court or by right. Depending on the type of case and the decision below, appellate review primarily consists of: an entirely new hearing (a non "trial de novo"); a hearing where the appellate court gives deference to factual findings of the lower court; or review of particular legal rulings made by the lower court (an appeal on the record). Under Article Three of the United States Constitution, the judicial power of the United States is vested in the Supreme Court of the United States and the inferior courts established by law. The Federal Rules of Appellate Procedure govern appellate proceedings. Under its standard of review, an appellate court decides the extent of the deference it would give to the lower court's decision, based on whether the appeal was one of fact or one of law. In reviewing an issue of fact, an appellate court ordinarily gives deference to the trial court's findings. It is the duty of trial judges or juries to find facts, view the evidence firsthand, and observe witness testimony. When reviewing lower decisions on an issue of fact, courts of appeal generally look for clear error. The appellate court reviews issues of law de novo (anew, no deference) and may reverse or modify the lower court's decision if the appellate court believes the lower court misapplied the facts or the law. An appellate court may also review the lower judge's discretionary decisions, such as whether the judge properly granted a new trial or disallowed evidence. The lower court's decision is only changed in cases of an "abuse of discretion". This standard tends to be even more deferential than the "clear error" standard. Before hearing any case, the Court must have jurisdiction to consider the appeal. Mandatory appellate jurisdictions must hear all properly filed appeals. Discretionary appellate jurisdictions may pick and choose which cases are to be reviewed again and again.