485 U.S. 681 (1988)
Huddleston v. United States is the Supreme Court's leading interpretation of Federal Rule of Evidence 404(b), which governs the admissibility of a defendant's other crimes, wrongs, or acts offered for non-propensity purposes such as knowledge, intent, or absence of mistake.
Under Federal Rules of Evidence 404(b) and 104, must a trial court make a preliminary finding by a preponderance of the evidence that the defendant committed the other act before admitting it, or is it sufficient that the court finds a jury could reasonably conclude, by a preponderance, that the other act occurred and the defendant committed it?
Rule 404(b) permits admission of other-acts evidence for non-propensity purposes (such as proving motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident) and excludes it when offered solely to prove character to show action in conformity therewith. The admissibility of such evidence is governed by Rule 104(b)'s conditional relevance standard: the judge does not make a preponderance finding of the other act but asks whether the evidence is sufficient for a reasonable jury to find, by a preponderance, that the other act occurred and that the defendant committed it. Even when offered for a proper purpose and supported under Rule 104(b), the evidence remains subject to Rule 403 balancing (probative value must not be substantially outweighed by unfair prejudice, confusion, or waste of time), and—upon request—Rule 105 requires a limiting instruction directing the jury to the proper, non-propensity use.
No judicial preponderance finding is required. Other-acts evidence offered under Rule 404(b) is admissible if there is sufficient evidence for a reasonable jury to find, by a preponderance, that the other act occurred and that the defendant committed it (Rule 104(b)), and if the evidence is offered for a proper 404(b) purpose and survives Rule 403 balancing, with a limiting instruction upon request.
Huddleston is the cornerstone case on Rule 404(b). It sets the national standard that other-acts evidence is governed by Rule 104(b)'s conditional relevance test, not a heightened or judicial preponderance threshold. It frames 404(b) as a rule of inclusion while insisting on layered protections: proper purpose, sufficiency for a reasonable jury to find the act occurred, Rule 403 balancing, and limiting instructions. The case also underscores the abuse-of-discretion standard governing appellate review of 404(b) rulings. For law students, Huddleston provides the analytic template for spotting and resolving 404(b) issues on exams and in practice: articulate the permitted purpose, assess sufficiency under 104(b), conduct robust 403 balancing (considering similarity, temporal proximity, and necessity), and specify the limiting instruction.