Overbreadth in criminal liability rules, especially in federal law, is abundant and much lamented. Overbreadth is avoidable if it results from normative mistakes about how much conduct to criminalize or from insufficient care to limit open texture in statutes. Social planners cannot so easily avoid overbreadth if they cannot reach behaviors for which criminalization is well justified without also reaching behaviors for which it is not. This mismatch problem is acute if persons engaging in properly criminalized behaviors deliberately alter their conduct to avoid punishment and have resources to devote to avoidance efforts. In response to such efforts, legal actors are apt to expand liability rules further, feeding a cycle of evasion and overbreadth that characterizes important areas of contemporary criminal law. Lawmakers cannot purge the resulting overbreadth from liability rules without producing underbreadth, at significant cost to regulatory objectives. I conclude that, in some areas of expanding substantive criminal law, answers to “overcriminalization” therefore lie not in reducing the scope of conduct rules but in greater reliance on mens rea doctrines, redesign of enforcement institutions, and modification of sentencing practices.