The Pakistan government launched a nuclear power programme in the mid1950s. At the time of launching the programme, there was no evidence that it intended to build nuclear weapons. In the 1960s, however, Pakistani attitude towards nuclear weapons modified slightly and the country adopted a ‘nuclear option’ policy, which meant that it reserved the choice to build nuclear weapons in the future. The adoption of a nuclear option policy was manifested in Pakistan’s decision not to sign the Non-Proliferation Treaty (NPT) in 1968. In the 1970s, Pakistan initiated, albeit clandestinely, a nuclear weapons programme and by the late 1980s, it acquired the capability to build nuclear weapons. The programme eventually culminated into the May 1998 open nuclear tests and the rise of a de facto nuclear weapons state. Since 1998, Islamabad has continuously upgraded and expanded its nuclear arsenal in order to maintain the credibility of its nuclear deterrence vis-à-vis its archrival India, which it perceives crucial for the survival of the Pakistani state. Against the above backdrop, this chapter addresses three issues: (1) why did Pakistan build nuclear weapons and what proliferation lessons does the Pakistani case generate; (2) what impact did the May 1998 nuclear tests and the rise of Pakistan as a de facto nuclear weapons state make on the global non-proliferation regime; and (3) can Pakistan be brought under the non-proliferation fold?