The Budapest Memorandum on Security Assurances comprises four substantially identical political agreements signed at the Conference on Security and Co-operation in Europe (CSCE) in Budapest, Hungary, on 5 December 1994, to provide security assurances by its signatories relating to the accession of Belarus, Kazakhstan and Ukraine to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The four memoranda were originally signed by four nuclear powers: Ukraine, Russia, the United States, and the United Kingdom. France and China gave individual assurances in separate documents.

The memoranda, signed in Patria Hall at the Budapest Congress Center [de; hu] with U.S. Ambassador Donald M. Blinken amongst others in attendance, prohibited Russia, the United States, and the United Kingdom from threatening or using military force or economic coercion against Ukraine, Belarus, and Kazakhstan, "except in self-defence or otherwise in accordance with the Charter of the United Nations". As a result of the memorandum and other agreements, between 1993 and 1996, Belarus, Kazakhstan, and Ukraine gave up their nuclear weapons. On 6 December the CSCE without mentioning the Budapest Memoranda per se published in the same conference hall the Budapest Summit Declaration and the Budapest Decisions, following which on 1 January 1995 it became known as the OSCE.

Russia violated the Budapest memorandum in 2014 with its annexation of Ukraine's Crimea and in 2022 by invading Ukraine. As a response, the United States, United Kingdom, and France provided Ukraine with financial and military assistance, and imposed economic sanctions on Russia, while ruling out "any direct interventions to avoid a direct confrontation with Russia".

According to the three memoranda, Russia, the U.S., and the U.K. confirmed their recognition of Belarus, Kazakhstan, and Ukraine becoming parties to the Treaty on the Non-Proliferation of Nuclear Weapons and effectively removing all Soviet nuclear weapons from their soil, and that they agreed to the following:

Partly as a way to gain international recognition, the Ukrainian government made commitments early on that Ukraine would be a non-nuclear-weapon state. The Declaration of State Sovereignty of Ukraine on 16 July 1990 committed Ukraine "not to accept, produce, or acquire nuclear weapons", although this was opposed by some Ukrainian politicians, who saw Russia as a threat. Until Ukraine transferred the Soviet nuclear weapons stationed on its soil, it held the world's third-largest nuclear weapons stockpile. Belarus only had mobile missile launchers, and Kazakhstan had chosen to quickly give up its nuclear warheads and missiles to Russia. Ukraine went through a period of internal debate on their approach.

On 23 May 1992, Russia, the U.S., Belarus, Kazakhstan, and Ukraine signed the Lisbon Protocol to the START I treaty, ahead of ratifying the treaty later. The protocol committed Belarus, Kazakhstan and Ukraine to adhere to the NPT as non-nuclear weapons states as soon as possible. However, the terms for the transfer of the nuclear warheads were not agreed, and some Ukrainian officials and parliamentarians started to discuss the possibility of retaining some of the modern Ukrainian built RT-23 (SS-24) missiles and Soviet built warheads.

In 1993, two regiments of UR-100N (SS-19) missiles in Ukraine were withdrawn to storage because warhead components were past their operational life, and Ukraine's political leadership realised that Ukraine could not become a credible nuclear military force, as they could not maintain the warheads and ensure long-term nuclear safety. Later in 1993, the Ukrainian and Russian governments signed a series of bilateral agreements giving up Ukrainian claims to the nuclear weapons and the Black Sea Fleet, in return for $2.5 billion of gas and oil debt cancellation and future supplies of fuel for its nuclear power reactors. Ukraine agreed to ratify the START I and NPT treaties promptly. This caused severe public criticism, leading to the resignation of Ukrainian Defence Minister Morozov. On 18 November 1993, the Rada passed a motion agreeing to START I but renouncing the Lisbon Protocol, suggesting that Ukraine would only decommission 36% of missile launchers and 42% of the warheads on its territory, and demanded financial compensation for the tactical nuclear weapons removed in 1992. This caused U.S. diplomatic consternation, and the following day Ukrainian President Kravchuk said: "we must get rid of [these nuclear weapons]. This is my viewpoint from which I have not and will not deviate." He then brought a new proposal to the Rada.

On 15 December 1993, U.S. Vice President Al Gore visited Moscow for a meeting. Following side discussions, a U.S. and Russian delegation, including U.S. Deputy Secretary of Defense William J. Perry, flew to Ukraine to agree to the outlines of a trilateral agreement including U.S. assistance in dismantling the nuclear systems in Ukraine and compensation for the uranium in nuclear warheads. Participants were invited to Washington on 3–4 January to finalise the agreement. A Trilateral Statement with a detailed annex was agreed, based on the previously agreed terms but with detailed financial arrangements and a firm commitment to an early start to the transfer of at least 200 warheads to Russia and the production in Russia of nuclear reactor fuel for Ukraine. Warheads would be removed from all RT-23s (SS-24) within 10 months. However, Ukraine did not want a commitment to transfer all warheads by 1 June 1996 to be made public for domestic political reasons, and Russia did not want the financial compensation for uranium made public because they were concerned that Belarus and Kazakhstan would also demand this. It was decided to exclude these two matters from the published agreement, but cover them in private letters between the countries' presidents.