The Treaty on Friendship, Cooperation, and Partnership between Ukraine and the Russian Federation, also known as the "Big Treaty",[2][3] 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.

[4] 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.

Under Article 2:In accord with provisions of the UN Charter and the obligations of the Final Act on Security and Cooperation in Europe, the High Contracting Parties shall respect each other′s territorial integrity and reaffirm the inviolability of the borders existing between them.

On 3 December 2018, Poroshenko drafted a legislation to Parliament to end the Treaty of Friendship immediately; support came from Western allies within the United Nations Security Council.

[20] Russia's Ministry of Foreign Affairs said that it was notified on 24 September 2018 of the treaty's termination by Ukraine and expressed regret.