A popular misconception is that cases are always appealed. Not often does a losing party have an automatic right of appeal. In a civil case, either party may appeal to a higher court. In a criminal case, only the defendant has a right to an appeal in most states. These appeals usually occur before the actual trial begins.
Criminal defendants convicted in state courts have a further safeguard.
After using all of their rights of appeal on the state level, they may file a writ of habeas corpus in the federal courts in an attempt to show that their federal constitutional rights were violated. The right of a federal review imposes the check of the federal courts on abuses that may occur in the state courts. An appeal is not a retrial or a new trial of the case. The appeals courts do not usually consider new witnesses or new evidence. Appeals in either civil or criminal cases are usually based on arguments that there were errors in the trial's procedure or errors in the judge's interpretation of the law.