Pakistan has a nuclear weapons stockpile of 130–140 warheads and appears to have plans to increase its arsenal further. With several delivery systems in development, four plutonium production reactors, and expansion of uranium enrichment facilities, the country’s stockpile will likely increase over the next 10 years, but by how much will depend on many things. Two key factors will be how many nuclear-capable launchers Islamabad plans to deploy, and how much the Indian nuclear arsenal grows. Based on Pakistan’s performance over the past 20 years and its current and anticipated weapons deployments, the authors estimate that its stockpile could potentially grow to 220–250 warheads by 2025, making it the world’s fifth-largest nuclear weapon state. Pakistan’s deployment of short-range, so-called tactical nuclear weapons is causing considerable concern in South Asia and in the US Government about warhead security and lowering of the threshold for nuclear weapons use.