• The Treaty on the Non-Proliferation of Nuclear Weapons, commonly known as the Non-Proliferation Treaty or NPT, is an international treaty whose objective is to prevent the spread of nuclear weapons and weapons technology, to promote cooperation in the peaceful uses of nuclear energy, and to further the goal of achieving nuclear disarmament and general and complete disarmament. 
• Between 1965 and 1968, the treaty was negotiated by Eighteen Nation Committee on Disarmament, a United Nations-sponsored organization based in Geneva, Switzerland.
• Opened for signature in 1968, the treaty entered into force in 1970. As required by the text, after twenty-five years, NPT Parties met in May 1995 and agreed to extend the treaty indefinitely. 
• More countries have adhered to the NPT than any other arms limitation and disarmament agreement, a testament to the treaty’s significance.  
• As of August 2016, 191 states have adhered to the treaty, though North Korea, which acceded in 1985 but never came into compliance, announced its withdrawal from the NPT in 2003, following detonation of nuclear devices in violation of core obligations. 
• Four UN member states have never accepted the NPT, three of which are thought to possess nuclear weapons: India, Israel, and Pakistan. In addition, South Sudan, founded in 2011, has not joined.
• The treaty defines nuclear-weapon states as those that have built and tested a nuclear explosive device before 1 January 1967; these are the United States, Russia, the United Kingdom, France, and China.
• Four other states are known or believed to possess nuclear weapons: India, Pakistan, and North Korea have openly tested and declared that they possess nuclear weapons, while Israel is deliberately ambiguous regarding its nuclear weapons status.

The NPT consists of a preamble and eleven articles. Although the concept of “pillars” is not expressed anywhere in the NPT, the treaty is nevertheless sometimes interpreted as a three-pillar system,  with an implicit balance among them:

1. non-proliferation,
2. disarmament, and
3. the right to peacefully use nuclear technology.

• These pillars are interrelated and mutually reinforcing. An effective nonproliferation regime whose members comply with their obligations provides an essential foundation for progress on disarmament and makes possible greater cooperation on the peaceful use of nuclear energy.
• With the right to access the benefits of peaceful nuclear technology comes the responsibility of nonproliferation. Progress on disarmament reinforces efforts to strengthen the nonproliferation regime and to enforce compliance with obligations, thereby also facilitating peaceful nuclear cooperation. The “pillars” concept has been questioned by some who believe that the NPT is, as its name suggests, principally about nonproliferation, and who worry that “three pillars” language misleadingly implies that the three elements have equivalent importance.
• There are eight sovereign states that have successfully detonated nuclear weapons.
• Five are considered to be nuclear-weapon States (NWS) under the terms of the Treaty on the Non-Proliferation of Nuclear Weapons(NPT).
• In order of acquisition of nuclear weapons these are: the United States, Russia (the successor state to the Soviet Union), the United Kingdom, France, and China.
• Since the NPT entered into force in 1970, three states that were not parties to the Treaty have conducted nuclear tests, namely India, Pakistan, and North Korea. North Korea had been a party to the NPT but withdrew in 2003.