The sanctions regimes employed by the United States are often painted with a broad brush as unlawful. Those who look a bit closer generally concede that US sanctions that apply on US territory and to US citizens are probably lawful. However, the conclusion usually follows that US sanctions with extraterritorial effect, and especially “secondary” sanctions that target, or at least encompass, foreign actors completely outside US jurisdiction, must surely be unlawful. Such arguments are generally based on appeals to principles of international law such as non-intervention, sovereignty, and jurisdiction. Few authors delve into actual US sanctions law and enforcement actions in any detail or depth. This chapter proposes to do precisely that by examining some of the main examples used to challenge the lawfulness of US sanctions, including BNP Paribas’ notorious $8.9 billion settlement with the US and direct challenges to the extraterritorial application of US secondary sanctions in the US case against Reza Zarrab. By closely examining US sanctions law and enforcement cases, the chapter argues that neither the principle of non-intervention nor the international law of jurisdiction is a persuasive basis for challenging the lawfulness of US secondary sanctions.