“Proxy crimes” is a phrase loosely used to refer to conduct that is punished only as a means to target other harmful conduct. Many criminal law scholars find the criminalization of this type of conduct unjustifiable from a retributivist perspective, while others note that proxy criminalization can contribute to mass incarceration and overcriminalization. Given the importance of these problems, a systematic analysis of proxy crimes, currently absent in the criminal law literature, is needed. In this article, we provide a comprehensive analysis of proxy crimes by (i) surveying the existing literature and identifying gaps in prior analyses, (ii) proposing a simple yet useful definition of proxy crimes, (iii) identifying three specific categories of proxy crimes, and (iv) conducting an economic analysis of proxy criminalization which allows us to identify conditions under which proxy criminalization is socially (un)desirable. Finally, in light of our analysis, we present and discuss a specific affirmative defense that can be made available to defendants charged with a proxy crime. We explain how legislators can better balance the social benefits and detriments of proxy criminalization through that affirmative defense.