The US Supreme Court’s 2018 decision in South Dakota v. Wayfair, Inc. dramatically expanded the subnational states’ power to require remote suppliers to collect taxes on in-bound sales to local consumers by repudiating the pre-existing, judicially created constitutional rule limiting the states’ authority to enforce such collection obligations to those suppliers with an in-state physical presence and replacing it with a ‘nexus’ rule based on ‘economic and virtual contacts’. The state legislatures reacted quickly and almost unanimously to the Wayfair decision by adopting rules imposing sales tax collection obligations on remote suppliers whose sales exceeded specified dollar or transaction thresholds. The states have imposed similar obligations on marketplace platforms that increasingly facilitate online cross-border sales. In principle, these post-Wayfair tax collection obligations imposed on remote suppliers apply equally to interstate and international cross-border sales and to domestic and foreign suppliers. As a practical matter, however, the states confront greater challenges in enforcing these obligations in the international context. Under the US Constitution’s ‘Full Faith and Credit Clause’, judgments against domestic suppliers that fail to comply with a state’s tax collection obligations may be enforced against such suppliers in other states where the suppliers are located. By contrast, under the so-called ‘revenue rule’ that is widely respected in the international context, judgments against foreign suppliers generally may not be enforced in the foreign suppliers’ home jurisdiction. Despite differences in the legal and practical mechanisms available to state tax authorities in enforcing tax obligations upon foreign as distinguished from domestic suppliers, states nevertheless have a variety of tools at their disposal to enforce or encourage tax collection by foreign suppliers, and there are other reasons why foreign suppliers may choose to comply with state collection requirements with respect to online sales.