Following an overview of the modern interest in deterrence, this chapter discusses the relationship between State-administered legal and formal sanctions including arrest, fines, and imprisonment and various informal sanctions and extralegal factors, ranging from the strength of an individual's moral commitment to abiding by the law to the pressure exerted by family members and friends to bow to convention. Another conceptual distinction that figures prominently in the debate is the difference between actual or objective deterrence effects and perceptual or subjective deterrence effects. A third concept to be considered is the difference between absolute and marginal deterrence. This chapter includes a literature review focusing on research findings related to the effectiveness of punishments as general and specific deterrents. Based on this review, the author concludes that apprehension and punishment are moderately effective in achieving deterrence, that the certainty of punishment is a more important factor in deterring crime than the severity of punishment, that individual perceptions play a determining role in deterring crime, and that chronic offenders are usually not deterred by well-publicized, anti-crime campaigns.