Cite as: 520 U. S. 259 (1997)
Opinion of the Court
Clauses bar legislatures from making substantive criminal offenses retroactive). In each of these guises, the touch-stone is whether the statute, either standing alone or as construed, made it reasonably clear at the relevant time that the defendant's conduct was criminal.
We applied this standard in Screws v. United States, 325 U. S. 91 (1945), which recognized that the expansive language of due process that provides a basis for judicial review is, when incorporated by reference into § 242, generally ill suited to the far different task of giving fair warning about the scope of criminal liability. The Screws plurality identified the affront to the warning requirement posed by employing § 242 to place "the accused . . . on trial for an offense, the nature of which the statute does not define and hence of which it gives no warning." Id., at 101. At the same time, the same Justices recognized that this constitutional difficulty does not arise when the accused is charged with violating a "right which has been made specific either by the express terms of the Constitution or laws of the United States or by decisions interpreting them." Id., at 104. When broad constitutional requirements have been "made specific" by the text or settled interpretations, willful violators "certainly are in no position to say that they had no adequate advance notice that they would be visited with punishment. . . . [T]hey are not punished for violating an unknowable something." Id., at 105. Accordingly, Screws limited the statute's coverage to rights fairly warned of, having been "made specific" by the time of the charged conduct. See also Kozminski, supra, at 941 (parallel construction of § 241).6
6 This process of "making specific" does not, as the Sixth Circuit believed, qualify Screws as "the only Supreme Court case in our legal history in which a majority of the Court seems [to have been] willing to create a common law crime." 73 F. 3d 1380, 1391 (1996). Federal crimes are defined by Congress, not the courts, Kozminski, 487 U. S., at 939; United States v. Wiltberger, supra, at 95, and Screws did not "create a common
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