Punishment plays a major function in preventing crime. Punishment can potentially shape criminal conduct through at least 13 different mechanisms: 5 have a positive effect, reducing crime, and 8 have a negative effect, stimulating offending. This article explains what these 13 potential effects of punishment are and how they have been theorized. It further reviews the body of available empirical evidence for each of these mechanisms. It finds that for many mechanisms there is mixed and inconclusive evidence with major methodological challenges. The article further analyzes the conditions under which punishment affects crime, including the type of crime, offender, and underlying causes and correlates of crime. It also explores the time frames through which punishment affects crime, as well as the ways in which different behavioral effects of punishment interact. The conclusion develops ideas about how this body of empirical work can come to shape criminal justice practice.