Orthodox thought holds that criminalisation should be subject to a wrongness constraint: that is, that conduct may be criminalised only if it is wrongful. This article argues that this principle is false, at least as it is usually understood. On the one hand, the wrongness constraint seems to rest on solid foundations. To criminalise conduct is to facilitate its condemnation and punishment; to coerce citizens against it; and to portray it as wrongful. All of these actions are presumptively impermissible when (...) the conduct that they target is not wrongful. On the other hand, the article argues that the wrongness constraint is nevertheless unsound. Although it is presumptively impermissible to criminalise non-wrongful conduct, this might yet be permissible, given sufficient countervailing reasons. Moreover, there are realistic cases – specifically, some cases of over-inclusive criminalisation – in which such countervailing reasons exist. (shrink)