Three factors are identified as affecting the probative value of other-crimes evidence: (1) its relationship to other evidence available to the prosecution, (2) the strength of the inference the factfinder is asked to draw from the evidence of other crimes, and (3) whether it is true. The importance of trial judges' balancing the magnitude of probative value against prejudicial effect to determine admissibility is highlighted, and a two-step process is recommended. First, the judge should balance under Rule 403 as though proof of the other crime were certain. If it appears tentatively admissible, the judge should consider the degree to which the other crime has been proved and strike a second balance between probative value and unfair prejudice. United States v. Beechum, one of the leading cases on the admissibility of other-crimes evidence, is examined, and other court decisions involving unfair prejudice and proof problems are addressed. Finally, it is emphasized that a judge is nearly always called upon by Rule 403 to weigh the probative value of other-crimes evidence against the danger of unfair prejudice and other misuse. The importance of this sliding scale of proof is highlighted. Included is a list of 150 references.