A Practice Note providing an overview of the antiboycott laws enforced by the US Commerce Department and the Internal Revenue Service, including the Anti-Boycott Act of 2018 and the Ribicoff Amendment to the 1976 Tax Reform Act (codified in Section 999 of the Internal Revenue Code). Together, these laws encourage and, in some cases, require US individuals and companies to refuse to participate in or cooperate with foreign boycotts that are not sanctioned by the US government, for example, the Arab League boycott of Israel. These laws also contain significant reporting requirements and impose significant criminal, civil, and tax penalties for non-compliance.