Mass surveillance is the intricate surveillance of an entire or a substantial fraction of a population in order to monitor that group of citizens. The surveillance is often carried out by local and federal governments or governmental organizations, but it may also be carried out by corporations (either on behalf of governments or at their own initiative). Depending on each nation's laws and judicial systems, the legality of and the permission required to engage in mass surveillance varies. It is the single most indicative distinguishing trait of totalitarian regimes. It is often distinguished from targeted surveillance.
Mass surveillance has often been cited by agencies like the National Security Agency (NSA) as necessary to fight terrorism, prevent crime and social unrest, protect national security, and control the population. At the same time, mass surveillance has equally often been criticized for violating privacy rights, limiting civil and political rights and freedoms, and being illegal under some legal or constitutional systems. Another criticism is that increasing mass surveillance could potentially lead to the development of a surveillance state, an electronic police state, or a totalitarian state wherein civil liberties are infringed or political dissent is undermined by COINTELPRO-like programs.