The rapid expansion of federal criminal law, beyond almost all prudential and constitutional limits, may not be the first thing to leap to mind when one thinks of key problems with American criminal law. But the existence now of over 4,450 federal criminal offenses is itself a problem that implicates the foundations of the criminal law. The number of federal offenses is too great for Americans to be familiar with all of the conduct that is criminal, and many of the offenses themselves are deeply flawed, omitting essential substantive elements necessary to protect the innocent.