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Defendants frequently attach supporting materials to Rule 12(b)(6) motions to dismiss for failure to state a claim. The plain text of Federal Rule of Civil Procedure 12(d) dictates that judges must either exclude this material or treat the motion as one for summary judgment. However, a substantial exception has emerged that threatens to swallow the rule. 

The exception, called incorporation by reference, permits the consideration of outside materials when they are either referenced in the pleadings, central to the claim, or sometimes both. Courts have defined these elements differently and have diverged in their understandings of the doctrine. Incorporation by reference appealingly offers an expedient route to resolve cases. But it also skirts the text and intention of the Federal Rules. This Comment explores the history of Rule 12(d), describes courts’ varying uses of the exception, and proposes a unifying method of interpretation for the future. Drawing on other procedural rules and an analogous doctrine in contract law, it argues that only unmistakably referenced written instruments may be incorporated.