In a non-jury trial the fact-finder is one or more professional judges rather than a jury of the defendant's 'peers'.
In common law jurisdictions, all trials in equity, of petty criminal offenses and violations, and of small claims at law are non-jury trials, also known as bench trials, held before a single judge. In all other cases, whether criminal charges and civil claims at law, the defendant may also waive a jury and be subject to a bench trial.
In civil law systems where juries are unknown, all trials are held before a judge or panel of judges.
Judges in non-jury trials serve dual roles, ruling on applicable law, including the rules of evidence and procedure, and as finders of fact. While lay juries are not trusted to be exposed to prejudicial inadmissible evidence, which may be grounds for a mistrial, judges in a non-jury trial may review all proffered materials while excluding from consideration any evidence that they determine to be inadmissible under the law.