The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) was signed in 1968 and entered into force on 5 March 1970. The NPT is often described as the cornerstone of the nuclear non-proliferation regime. The Treaty on the Non-Proliferation of Nuclear Weapons recognised five states as nuclear-weapon states (NWS): China, France, the Soviet Union (succeeded by the Russian Federation in 1991), the United Kingdom and the United States of America. Each of these five states is committed not to transfer nuclear weapons or control over them to any other state. There are currently 187 recognised states that are party to the treaty.
You can read the background to the Treaty and the actual text:
All other states must adhere to the Treaty as non-nuclear-weapon states (NNWS). These states are obliged not to manufacture or otherwise acquire nuclear weapons and to accept International Atomic Energy Agency (IAEA) safeguards on all their nuclear material. The right to the development and use of civil nuclear power is enshrined in the NPT, and safeguards are designed to detect any diversion of nuclear material from declared peaceful uses.
All parties, including the NWS parties, also undertake "to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control".
The NPT contained a provision requiring a Review Conference (RevCon) to be held five years after its entry into force and enabling such conferences to be held at five yearly intervals thereafter to review the operation of the Treaty. The most recent RevCon was held in New York in May 2010.