Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people and often in a surreptitious manner. It most usually refers to observation of individuals or groups by government organizations, butdisease surveillance, for example, is monitoring the progress of a disease in a community.

The word surveillance is the French word for "watching over".

The word surveillance may be applied to observation from a distance by means of electronic equipment (such as CCTV cameras), or interception of electronically transmitted information (such as Internet traffic or phone calls). It may also refer to simple, relatively no- or low-technology methods such as human intelligence agents and postal interception.

Surveillance is very useful to governments and law enforcement to maintain social control, recognize and monitor threats, and prevent/investigate criminal activity. With the advent of programs such as the Total Information Awareness program and ADVISE, technologies such as high speed surveillance computers and biometrics software, and laws such as the Communications Assistance For Law Enforcement Act, governments now possess an unprecedented ability to monitor the activities of their subjects.

However, many civil rights and privacy groups such as the Electronic Frontier Foundationand ACLU have expressed concern that by allowing continual increases in government surveillance of citizens that we will end up in a mass surveillance society, with extremely limited, or non-existent political and/or personal freedoms.