Surveillance ( /sərˈveɪ.əns/ or /sərˈveɪləns/) is the monitoring of the behavior, activities, or other changing information, usually of people for the purpose of influencing, managing, directing, or protecting. Surveillance is therefore an ambiguous practice, sometimes creating positive effects, at other times negative. It is sometimes done in a surreptitious manner. It most usually refers to observation of individuals or groups by government organizations, but disease 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.

Glenn Greenwald (born March 6, 1967) is an American lawyer, columnist, blogger, and author. Greenwald worked as a constitutional and civil rights litigator before becoming a contributor (columnist and blogger) to Salon.com, where he focuses on political and legal topics. He has also contributed to other newspapers and political news magazines, including The New York Times,The Los Angeles Times,The Guardian,The American Conservative,The National Interest, and In These Times.

Greenwald has written four books, three of which have been New York Times bestsellers: How Would a Patriot Act? (2006); A Tragic Legacy (2007), and With Liberty and Justice for Some: How the Law Is Used to Destroy Equality and Protect the Powerful, released in October 2011. He also wrote Great American Hypocrites (2008).

In March 2009, he was selected, along with Amy Goodman of Democracy Now!, as the recipient of the first annual Izzy Award by the Park Center for Independent Media, an award named after independent journalist I.F. "Izzy" Stone and devoted to rewarding excellence in independent journalism. The selection panel cited Greenwald's "pathbreaking journalistic courage and persistence in confronting conventional wisdom, official deception and controversial issues."