Harmless Error

Harmless error is a mistake in a trial or agency proceeding that an appellate court disregards because it did not affect the substantial rights of the parties. Under 28 U.S.C. § 2111, courts of appeals must give judgment “after an examination of the record, without regard to errors or defects that do not affect the substantial rights of the parties.” The doctrine prevents outcomes from being reversed for technical mistakes.

Example: In Rose v. Clark (1986), the Supreme Court held that a constitutionally defective jury instruction did not require reversing a conviction, because the prosecution proved beyond a reasonable doubt that the error was harmless (478 U.S. 570).

Common misconception: Not every error is harmless. Some — the Supreme Court said in Rose v. Clark that it has treated a limited few this way — are structural and require reversal regardless of the evidence, such as a complete denial of counsel.

Sources: 28 U.S.C. 2111 Harmless error | uscode.house.gov; Rose v. Clark, 478 U.S. 570 (1986) | U.S. Reports (Library of Congress)