Pakistan confronts numerous domestic security challenges including jihadist extremism, Sunni-Shi'a sectarian violence, drug trafficking, illegal commodity smuggling, endemic corruption, and systemic problems with the provision of justice and law enforcement. While much has been written about US military assistance to the Government of Pakistan (GOP) and the ever-evolving political relations between the two countries, basic questions of highest policy significance related to Pakistan's internal security have never been fully studied or considered. This essay begins to address these empirical lacunae. It first provides a comprehensive examination of Pakistan's internal security environment and the effectiveness of the GOP's criminal justice structures in dealing with these challenges. The paper then goes on to assess the impact and utility of the current suite of US law enforcement assistance in helping to fortify Pakistan's domestic security environment. The study raises a number of difficult questions pertinent to the long-term impact of this support, particularly in terms of its effect on fostering a viable, accountable and transparent system of civilian governance and policing.