Disarmament is the act of reducing, limiting, or abolishing weapons. Disarmament generally refers to a country's military or a specific type of weaponry. Disarmament is often taken to mean total elimination of weapons of mass destruction, such as nuclear arms. General and Complete Disarmament was defined by the United Nations General Assembly as the elimination of all weapons of mass destruction, coupled with the “balanced reduction of armed forces and conventional armaments, based on the principle of undiminished security of the parties with a view to promoting or enhancing stability at a lower military level, taking into account the need of all States to protect their security.”

At the Hague Peace Conferences in 1899 and 1907 government delegations debated about disarmament and the creation of an international court with binding powers. The court was considered necessary because it was understood that nation-states could not disarm into a vacuum. After World War I revulsion at the futility and tremendous cost of the war was widespread. A commonly held belief was that the cause of the war had been the escalating buildup of armaments in the previous half century among the great powers (see Anglo-German naval arms race). Although the Treaty of Versailles effectively disarmed Germany, a clause was inserted that called on all the great powers to likewise progressively disarm over a period of time. The newly formed League of Nations made this an explicit goal in the covenant of the league, which committed its signatories to reduce armaments 'to the lowest point consistent with national safety and the enforcement by common action of international obligations'.

One of the earliest successful achievements in disarmament was obtained with the Washington Naval Treaty. Signed by the governments of Great Britain, the United States, Japan, France, and Italy, it prevented the continued construction of capital ships and limited ships of other classification to under 10,000 tons displacement. The size of the three country's navies (the Royal Navy, United States Navy and Imperial Japanese Navy) was set at the ratio 5-5-3.

In 1921, the Temporary Mixed Commission on Armaments was set up by the League of Nations to explore possibilities for disarmament. It was made up not of government representatives but of famous individuals who rarely agreed. Proposals ranged from abolishing chemical warfare and strategic bombing to the limitation of more conventional weapons, such as tanks. A draft treaty was assembled in 1923 that made aggressive war illegal and bound the member states to defend victims of aggression by force. Since the onus of responsibility would, in practice, be on the great powers of the League, it was opposed by the First MacDonald ministry of the British government, whose opposition to the treaty, made official on 5 July 1924, "effectively buried the proposal for good."

Another commission in 1926, set up to explore the possibilities for the reduction of army size, met similar difficulties. However acting outside the League. French Foreign Minister Aristide Briand and US Secretary of State Frank Kellogg drafted a treaty known as the Kellogg–Briand Pact, which denounced war of aggression. There were 65 signatories to the pact, but it set out no guidelines for action in the event of a war. It was in 1946 used to convict and execute Nazi leaders of war crimes.

A final attempt was made at the Geneva Disarmament Conference from 1932 to 1937, chaired by former British Foreign Secretary Arthur Henderson. Germany demanded the revision of the Versailles Treaty and the granting of military parity with the other powers, while France was determined to keep Germany demilitarised for its own security. Meanwhile, the British and Americans were not willing to offer France security commitments in exchange for conciliation with Germany. The talks broke down in 1933, when Adolf Hitler withdrew Germany from the conference.

Nuclear disarmament refers to both the act of reducing or eliminating nuclear weapons and to the end state of a nuclear-free world, in which nuclear weapons are completely eliminated.

In the United Kingdom, the Campaign for Nuclear Disarmament (CND) held an inaugural public meeting at Central Hall, Westminster, on 17 February 1958, attended by five thousand people. After the meeting a few hundred left to demonstrate at Downing Street.