Russian–Ukrainian Friendship Treaty

The Treaty on Friendship, Cooperation, and Partnership between Ukraine and the Russian Federation, also known as the "Big Treaty", was an agreement signed in 1997 between Ukraine and Russia, which fixed the principle of strategic partnership, the recognition of the inviolability of existing borders, and respect for territorial integrity and mutual commitment not to use its territory to harm the security of each other. The treaty prevents Ukraine and Russia from invading one another's country respectively, and declaring war. Due to the beginning of the Russo-Ukrainian War in 2014, Ukrainian president Petro Poroshenko signed a decree not to extend the treaty on 19 September 2018. The treaty consequently expired on 31 March 2019.

Until 2019, the treaty was automatically renewed on each 10th anniversary of its signing, unless one party advised the other of its intention to end the treaty six months prior to the date of the renewal.

Russia–Ukraine relations have deteriorated since the start of the Russo-Ukrainian War with the 2014 Russian annexation of Crimea and Russian support for separatist forces in the war in Ukraine's Donbas region. They were completely severed following the Russian invasion of Ukraine.