The harmless error doctrine applies to cases involving the admissibility of?

The harmless error doctrine is concerned with the treatment of errors that arise out of trial proceedings. The Supreme Court has held that most constitutional errors do not mandate the automatic reversal of a conviction (as would have occurred under the reversal-per-se rule). This is largely due to the realization that most constitutional errors are completely harmless. Consequently, the Court held in Chapman v. California (1967) that only errors for which there is a realistic possibility of prejudice in the outcome would mandate automatic reversal. Otherwise, the error should be considered harmless and not sufficient grounds for reversal of the conviction.