Secondary sanctions are unique in their audacity. Their application in an interdependent global context raises the specter of an uncontrolled burn, with consequences stretching beyond even their broadest scope. Such consequences reshape markets and, at times, create new ones. This chapter uses Iran as a lens through which to examine the relationship between the informal economy and US secondary sanctions and the potential disruption provided by the proliferation of cryptocurrencies. The chapter ultimately concludes that despite much-heralded potential, cryptocurrency’s disruption to the US financial system’s supremacy, as well as the sanctions regimes reliant on such supremacy, remains, for now, limited. This incomplete disruption means that any blunting effect provided by cryptocurrency on secondary sanctions cannot fully protect the informal economies and the participants therein from the effects of such sanctions, particularly in more protracted sanctions regimes. Indeed, cryptocurrency’s likeliest role in US sanctions is not to upend the secondary sanctions regime but rather to complicate the enforcement process. Given its rapid proliferation and built-in cryptography, cryptocurrency is likely to continue to make enforcement of sanctions more difficult, more expensive, and, perhaps, less appealing to pursue all potential evaders.