Rule 23 of the Federal Rules of Civil Procedure governs the standards for certifying a class action, a type of litigation whose aggregate form is intended to make litigation accessible to large groups of injured plaintiffs and incentivize the vindication of claims that may otherwise go unpursued in the face of high litigation costs. However, while due process requires that a certifying court find that each element of Rule 23 is satisfied through “evidentiary proof,” the federal courts have failed to adopt any kind of consistent evidentiary standard to apply to the record proffered at class certification. This has resulted in the use of class certification as a bargaining chip between plaintiffs’ lawyers and wealthy defendants, rather than as a procedural mechanism that serves to test the propriety of a particular action for class treatment. Ultimately, this dynamic harms the very injured plaintiffs that this mechanism seeks to protect. This Note examines the need for a uniform evidentiary standard and surveys the countervailing interests of absent class members, defendants, class counsel, and the court at this critical juncture in a class action proceeding. It then proposes a novel categorization of the Federal Rules of Evidence as either form- or substance-based, and argues that an evidentiary standard that properly balances the interests of all parties involved in the class action requires a certifying court to apply substance-based evidence rules in determining whether a proposed class satisfies Rule 23. Such a rule, this Note will argue, is essential to ensuring that absent class members are protected, rather than exploited, by the class action mechanism.