A two-day nuclear security summit opens on Monday in Washington, gathering the international community to discuss securing vulnerable nuclear materials and preventing acts of nuclear terrorism.

The Comprehensive Nuclear Test Ban Treaty (CTBT) is one of the oldest items on the nuclear arms control agenda, though it has not entered into force yet since its adoption. The following is a brief introduction to the CTBT.

The Conference on Disarmament (CD) began its substantive negotiations on a comprehensive nuclear test ban treaty in January 1994 in Geneva, within the framework of an ad hoc committee established for the same purpose.

After more than two years of intensive negotiations, the committee presented a final draft treaty to the CD in June 1996. However, the submission of the treaty to the United Nations General Assembly was disapproved by India.

In August 1996, Australia requested the UN General Assembly to resume the treaty. The treaty was ultimately adopted by the General Assembly on Sept. 10, 1996, and opened for signatures in New York on Sept. 26 the same year.

The CTBT, which includes one preamble, 17 articles, two annexes and one protocol, is aimed at banning nuclear testing everywhere on the planet -- from the earth's surface, atmosphere, underwater to underground.

The CTBT stipulates signatories to continue systematic and progressive efforts to reduce nuclear weapons globally, with the ultimate goal of eliminating those weapons, and of general and complete disarmament under strict and effective international control.

The treaty also bans its signatories from carrying out any nuclear weapon test explosion or any other nuclear explosion, and restrains each state party from causing, encouraging, or in any way participating in the carrying out of any nuclear weapon test explosion or any other nuclear explosion.

In accordance with the articles of the treaty, it will enter into force 180 days after the 44 states listed in Annex 2 of the treaty have ratified it.

Currently, 151 states of a total of 182 member states have ratified the treaty, with 35 states listed in Annex 2 ratifying the treaty.