Penelitian ini menggunakan metode penelitian yuridis normatif melalui studi kepustakaan untuk meninjau bagaimana United Nations Convention on Contracts of the International Sale of Goods 1980 (CISG) mengatur keabsahan kontrak jual beli internasional. Pasal 4(a) CISG menyatakan bahwa CISG secara umum tidak mengatur permasalahan keabsahan, dengan pengecualian tertentu. Hasil penelitian ini menunjukkan bahwa CISG hanya mengatur keabsahan formil, initial impossibility of performance, dan open-price contracts. Sebagaimana terlihat dari kasus Forestal Guarani v. Daros International dan Geneva Pharmaceuticals v. Barr Laboratories, CISG mengatur bahwa permasalahan keabsahan yang tidak diaturnya akan diselesaikan menurut hukum yang berlaku berdasarkan Kaidah Hukum Perdata Internasional (HPI). Selain itu, penelitian ini juga membahas bagaimana instrumen internasional lainnya, Kaidah HPI Indonesia, serta Rancangan Undang-Undang HPI Indonesia mengatur keabsahan kontrak jual beli internasional.

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This research attempts to shed light on how the United Nations Convention on Contracts of the International Sale of Goods 1980 (CISG) regulates the validity of international sales contracts, using juridical normative research method through literature studies. According to Article 4(a) of the CISG, the Convention does not govern matters on validity, with certain exceptions. This research shows that CISG governs some matters pertaining to validity: formal validity, initial impossibility of performance, and open-price contracts. As seen from the cases of Forestal Guaraniv. Daros International and Geneva Pharmaceuticals v. Barr Laboratories, the CISG allocates those validity issues which do not fall under its purview to the applicable domestic law, as determined by Private International Law (PIL). Moreover, this research discusses how other international instruments, Indonesia’s PIL, and Indonesia’s Draft Law on PIL regulate validity issues.