The source of the veto
Article 27 of the Charter of the United Nations stipulates that resolutions can only be passed with the "affirmative vote of nine members [out of 15] including the concurring votes of the permanent members." The permanent members can thus block any resolution by voting against it. This is known as the "right of veto", although the word "veto" does not appear anywhere in the UN Charter.
The function of the veto
The right of veto was introduced by the authors of the Charter in order to ensure that the victors of World War II spoke with a single voice on matters of war and peace – and not to give each of them the means of blocking any resolution they chose. The Charter’s authors assumed that the victors would, on the whole, be willing to agree on appropriate action – but soon after the end of World War II it became clear that they were not.
During the East‑West confrontation, the right of veto thus played a rather negative role, and the criticism of this Charter provision – criticism which has endured to this day – was entirely justified. However, since the end of the Cold War, the right of veto has only been used sparingly. That is not to say it has become irrelevant. What tends to happen now is that permanent members threaten, more or less subtly, to use the veto in order to ensure that Security Council resolutions are drafted in line with their wishes or to prevent them from being put to a vote at all.
Non‑permanent members also have a right of veto
The fact that the non‑permanent members also have a kind of “collective right of veto” attracts less attention. If more than six members of the Security Council do not support a resolution, it will fail since there is no way in which it can obtain the nine votes required for a majority, even if all permanent members vote in favour. However, this happens very rarely.
Use of the right of veto
Ever since the founding of the United Nations, the permanent members have made use of their right of veto. Instances of its use can be counted in various ways. For example, if several permanent members vote against a draft resolution, this could be counted either as a single veto, or as several. Vetoes have also been used against individual paragraphs within resolutions, or against specific annexes.
The permanent members responsible for the greatest use of the veto have varied from one politico‑historical period to the next.