A foundational question in every dispute over intellectual property is whether the defendant’s product is too similar to the plaintiff ’s. For almost all intellectual property regimes, an extensive body of case law and academic commentary has examined how such similarity should be measured. Trade secrecy, however, remains a remarkable exception. In trade secrecy cases, just as in other intellectual property cases, the defendant’s good or method can diverge markedly from what the plaintiff developed. Yet it turns out that trade secret case law provides little guidance for assessing how much similarity is too much. The standard remains, fittingly but frustratingly, a secret.This Article takes the first close look at what that standard should ...