An appeal is a request to a higher (appellate) court for that court to review and change the decision of a lower court. Because post-trial motions requesting trial courts to change their own judgments or order new jury trials are so seldom successful, the defendant who hopes to overturn a guilty verdict must usually appeal. The defendant may challenge the conviction itself or may appeal the trial court's sentencing decision without actually challenging the underlying conviction. 

Appeals judges generally resist overruling trial court judgments and prefer to give trial judges wide discretion in the conduct of trials. As many appellate courts have said, defendants are not guaranteed "perfect" trials. Normally an appellate court will overturn a guilty verdict only if the trial court made an error of law that significantly contributed to the outcome. Put differently, an error by the trial judge will not lead to a reversal of a conviction as long as the error can reasonably be considered harmless. Not surprisingly, most errors are deemed "harmless," and consequently few convictions are reversed. However, some types of errors are so grievous that they are presumed harmful, such as the use of a coerced confession in violation of the 14th Amendment.

Sentences are a different matter. When the trial judge is given discretion over the sentence, the appellate court will rarely interfere. However, if the law requires a particular sentence and the judge gets it wrong, the appellate court will usually send the case back for resentencing.

In most modern American jurisdictions, a "writ" is an order from a higher court to a lower court or to a government official such as a prison warden. Defendants may seek several types of writs from appellate judges directed at the trial court or at a lower appellate court. (Many states have two levels of appellate courts -- an intermediate appellate court and the state supreme court.) 

Writs, like appeals, are complex and involve picky details. Defendants facing situations where they may be entitled to take a writ should consult counsel.

Writs usually are considered to be extraordinary remedies, meaning they are permitted only when the defendant has no other adequate remedy, such as an appeal. In other words, a defendant may take a writ to contest a point that the defendant is not entitled to raise on appeal. As a general rule, this applies to issues that are not apparent in the record of the case itself (such as when an attorney fails to investigate a possible defense).

Any one of the following reasons, for example, may prohibit an appeal (and justify a writ):

• The defense did not lodge a timely objection at the time of the alleged injustice (but should have).
• A final judgment has not yet been entered in the trial court, but the party seeking the writ needs relief at once to prevent an injustice or unnecessary expense.
• The matter is urgent. (Writs are heard more quickly than appeals, so defendants who feel wronged by actions of the trial judge may need to take a writ to obtain an early review by a higher court.)
• The defendant has already lodged an unsuccessful appeal (defendants may file multiple writs but the right to appeal is limited to one). But filing a writ that simply mimics an unsuccessful appeal is a frivolous writ and will be dismissed immediately.