This chapter begins by exploring the options that were open to regulators when crypto-assets emerged from obscurity to universal acceptance. Their misuse for cybercrime and laundering the proceeds of crime provoked a reaction from civil society. The chapter explores the international, supranational, and national approaches to defining the technology and the businesses that deal in it. Simply put, if a business falls within the legal definitions, it is subject to the entirety of the AML regime and the obligations that arise as a result. Differences in definitions mean that while the majority of the friction points between the real world and crypto-world are covered by some form of AML rules, there are many areas, especially on-chain activity within the crypto-world, outside regulation that offer criminals opportunities to launder their ill-gotten gains. The sufficiency of the controls put in place will be discussed in forthcoming chapters of this book.