Piagam Bangsa-Bangsa Bersatu adalah perjanjian asas organisasi antarabangsa dipanggil Pertubuhan Bangsa-Bangsa Bersatu.[1] Ia telah ditandatangani di Pusat Peringatan Perang San Francisco War Memorial dan Pusat Seni Pentas di San Francisco, Amerika Syarikat, pada Jun 26, 1945, oleh 50 dari 51 ahli asal (Poland, the other original member, which was not represented at the conference, signed it later). It entered into force on October 24, 1945, after being ratified by the five permanent members of the Security Council—the Republic of China (later replaced by the People's Republic of China), France, the Union of Soviet Socialist Republics (later replaced by the Russian Federation), the United Kingdom, and the United States—and a majority of the other signatories. Today, 192 countries are the members of the United Nations.