Warrantless surveillance

As the earliest electrically based communications, such as the telegraph and telephone, were introduced, governments became interested in the contents of communications. Depending on the legal system of the country, there might have been an assumption that interception, at least of one's own citizens' communications, needs some review and approval. In other countries, the rights of the state were considered greater than the rights of the society, and it made no difference if the reason for applying the techniques of communications intelligence was for reasons of military operational security (OPSEC), domestic law enforcement, ideological conformance, or maintenance of a national security state.

While some aspects fall under international telecommunications agreements, the scope of surveillance is generally defined on a nation-by-nation basis, and, even within a democracy, the level to which a right of privacy is accepted and under what circumstances its violation will be accepted. In some countries, such surveillance will be allowed only if a court or other independent review issues the orders. In other cases, a senior official may authorize it, but must make a formal statement of necessity, which potentially is available for future review.

The issue of privacy of communications actually goes back well before electrical communications technologies. Covert interception of written communications, copying their contents, and forwarding them on certainly existed in the Middle Ages. Even encrypted communications were being deciphered, such as by Sir Francis Walsingham, Elizabeth I's intelligence officer, in the late 16th century.

United States

Perhaps the first systematic legal analysis of a perceived need for warrants to intercept private communications was in the Communications Act of 1934.

• Communications Assistance to Law Enforcement Act (CALEA), 1994 [http:www.calea.org/ ]]
• Smith v. Maryland, 1979
• Foreign Intelligence Surveillance Act, 1978
• PATRIOT Act

Multinational

It is generally agreed that there is some type of multinational communications intelligence alliance that has been called ECHELON. It is generally agreed that it has involved Australia, Canada, New Zealand, the United Kingdon, and the United States. Its operations and current status, however, are not well understood, although it has been investigated by the European Parliament.