Criminological scholarship has long examined the ways that illicit goods and services are traded through underground economies, such as narcotics and stolen goods. In the last two decades, researchers have explored the ways that online spaces, such as forums, are used by actors to engage in the sale of digital goods, including stolen personal information and malicious software. Additionally, research has begun to explore the ways that a global network for the sale of drugs has emerged in online markets operating on the so-called Dark Web. Though these studies improve our understanding of the basic social structures that drive online transactions for various criminal services, myriad questions remain as to what drives engagement in online markets and the ways that they persist and evolve over time. This work provides an overview of the various illicit markets operating on the Open and Dark Web, and their relationship to open and closed economically-motivated illicit goods and services markets in the real world. This work also explores the range of research questions that must be addressed to improve our understanding of the actors who shape the processes of online markets, inclusive of buyers, sellers, and website operators. Keywords Illicit