Treaty on the Non-Proliferation of Nuclear Weapons
More often known as the Nuclear Nonproliferation Treaty (NPT), this treaty is correctly named the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) With the first signatures in 1968, the Treaty became active in 1970. A total of 187 parties have joined the Treaty, including the five nuclear-weapon States. An active UN organization, the International Atomic Energy Agency, works both with enforcement and the promotion of peaceful use of nuclear weapons.  Its actual language is reviewed at five-year intervals. 
After the ratification, states were only allowed to join the five nations, China, France, Soviet Union/Russia, United Kingdom, and United States that were "declaratory" and announced they had a nuclear arsenal they would keep. New signatories were expected to be "non-declaratory" and renounce having their own nuclear weapons. As a result, several nations that either have or are strongly suspected to have nuclear weapons have refused to sign as "non-declaratory" states: India, Israel, North Korea and Pakistan. One special case is South Africa, which built nuclear weapons but disarmed itself under secret international monitoring, and is a nondeclaratory signatory.
Article I obliges declaratory states not to transfer weapons to nondeclaratory states; Article II creates an obligation of nondeclaratory states not to receive them.
Each nuclear-weapon State Party to the Treaty undertakes not to transfer to any recipient whatsoever nuclear weapons or other nuclear explosive devices or control over such weapons or explosive devices directly, or indirectly; and not in any way to assist, encourage, or induce any non-nuclear-weapon State to manufacture or otherwise acquire nuclear weapons or other nuclear explosive devices, or control over such weapons or explosive devices.
Specific weapons proliferation
Permissive Action Link technology increases control of nuclear weapons. Nevertheless, PAL design depends on intimate knowledge of weapon design, and transfer of PAL technology to a nondeclaratory state may technically violate the NPT.
The treaty status of a nondeclaratory state discussing its weapons is also unclear. In an interview with Time Magazine, former senior Pakistani nuclear official Naeem Salik , who had been director of arms control and disarmament affairs at Pakistan's National Command Authority, said "Permissive action links are custom-made devices based on the design and configuration of the weapons...Unless one is willing to share the technical configuration of the weapon, a permissive action link cannot be developed. We did not share these secrets, so we never asked for the permissive action links — our people have developed our own." 
The United States has provided tactical nuclear weapons to NATO partners under "dual-key" arrangements, where both a U.S. and host nation action is required to arm the weapon. It is the U.S. position that because the U.S. retains control, it does not violate Article I and II.
This issue may become moot, as, in general, Western nations are finding less and less utility for tactical nuclear weapons. While a wide variety of weapons were once shared, the only ones now under such arrangements are B61 gravity bombs. It appears several countries may end the agreement and send back the bombs.
- United Nations, Brief Background
- United Nations, THE TREATY ON THE NON-PROLIFERATION OF NUCLEAR WEAPONS (NPT)
- Mark Thompson (24 April 2009), "Does Pakistan's Taliban Surge Raise a Nuclear Threat?", Time
- Otfried Nassauer (May 2001), Nuclear Sharing in NATO: Is it Legal?, Institute for Energy and Environmental Research