This article analyzes Pakistan's nuclear weapons program and the characteristics of the environment in which the program is nested. These characteristics include Pakistan's history of internal and external instability; nuclear saber rattling during crises; support for Islamic terrorism in order to advance state goals; indigenous production of many elements of its nuclear forces; possession of delivery and command and control systems with destabilizing characteristics; and finally, nuclear doctrine that appears to advocate first use of nuclear weapons. The article argues that the characteristics of Pakistan's nuclear weapons program generate threats to US national security interests. The article examines six interrelated and synergistic challenges for US national security: first, Pakistan is engaged in an arms race in Southwest Asia that has negative implications for Pakistan's stability; second, the threat of nuclear proliferation from Pakistan continues; third, Pakistan's arsenal characteristics make accidental and/or unauthorized nuclear war more likely; fourth, there is an ongoing possibility of war with India; fifth, Islamist influence is spreading through key sectors of Pakistani society; and finally, there is an increasing danger of state failure in Pakistan.