UNIDROIT (formally, the International Institute for the Unification of Private Law; French: Institut international pour l'unification du droit privé) is an intergovernmental organization whose objective is to harmonize international private law across countries through uniform rules, international conventions, and the production of model laws, sets of principles, guides and guidelines. Established in 1926 as part of the League of Nations, it was reestablished in 1940 following the League's dissolution through a multilateral agreement, the UNIDROIT Statute. As of 2019 UNIDROIT has 63 member states.

UNIDROIT has prepared multiple conventions (treaties), but has also developed soft law instruments. An example are the UNIDROIT Principles of International Commercial Contracts. Distinctly different from the Convention on the International Sale of Goods (CISG) adopted by UNCITRAL, the UNIDROIT Principles do not apply as a matter of law, but only when chosen by the parties as their contractual regime.