This chapter considers the question of how new non-criminal (or quasi-criminal) policies are altering the traditional criminal law approach to a range of social problems. While the contemporary debate on criminalization tends to focus exclusively on the problem of overcriminalization, there is a less conspicuous but by no means less pressing problem: the problem of undercriminalization. The chapter examines the social, political, and constitutional significance of the proliferation of civil preventive measures and argues that these measures may constitute undercriminalization insofar as they exclude appropriate procedural safeguards and other protections for the individual, which would be available if the preventive measures were classified as criminal. When this is the case, instances of undercriminalization pose no less a threat to individual liberty than overcriminalization, as they lead to intrusions upon individual liberty in the name of prevention without due procedural safeguards. The chapter concludes that, while it is certainly true that in many cases preventive measures are to be preferred over traditional criminal law approaches, there are also cases in which criminalization should be preferred.