Abstract: In his book, Defending the Undefendable, Walter Block (1976) makes the case that an individual counterfeiter of fiat notes does not commit a natural law crime, because money issued by the government is itself counterfeit. Several authors, including Murphy (2006), Machaj (2007), and Davidson (2010), have taken issue with Block’s argument. In Davidson (2010), I maintain that while the issuance and use of fiat currency by the state violates the natural law, fiat notes are not counterfeit, and their use by ordinary people is legitimate. The private counterfeiter is a thief when he exchanges his notes with these innocents, because they are rightful owners of both the fiat currency and the goods for which it is exchanged. Block (2010), in a rejoinder, disputes this on both ethical and utilitarian grounds. The present paper is a response to Block, and an elaboration of my original article. From a natural law perspective, I explore the ethical violations surrounding counterfeiting, and the legitimacy of producing and using fiat money by both the state and the individual.