The United Nations Convention on Contracts for the International Sale of Goods (CISG), sometimes known as the Vienna Convention is a multilateral treaty that establishes a uniform framework for international commerce. Ratified by 93 countries, known as "Contracting States", the Convention governs a significant proportion of world trade, making it one of the most successful instruments of international trade law. Guatemala and Laos are the most recent parties to the Convention, acceding to it on 12 December 2019 and 24 September 2019, respectively.

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The CISG was developed by the United Nations Commission on International Trade Law (UNCITRAL) beginning in 1968, drawing from previous efforts in the 1930s undertaken by the International Institute for the Unification of Private Law (UNIDROIT). In 1980, a draft text was introduced in a conference in Vienna, and following weeks of discussion and modification, it was unanimously approved and opened for ratification; the CISG subsequently came into force on 1 January 1988, after being ratified by 11 countries.

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The purpose of the CISG is to facilitate international trade by removing legal barriers among Contracting States. To that end, it establishes substantive rules that regulate the duties and obligations of both parties, including the delivery of goods, contract formation, and remedies for breach of contract. Unless expressly excluded by the contract, the CISG is incorporated by default into the domestic laws of Contracting States with respect to a transaction in goods between their nationals.