The system known as 'ECHELON' is an interception system which differs from other intelligence systems in that it possesses two features which make it quite unusual:

The first such feature attributed to it is the capacity to carry out quasi-total surveillance. Satellite receiver stations and spy satellites in particular are alleged to give it the ability to intercept any telephone, fax, Internet or e-mail message sent by any individual and thus to inspect its contents.

The second unusual feature of ECHELON is said to be that the system operates worldwide on the basis of cooperation proportionate to their capabilities among several states (the UK, the USA, Canada, Australia and New Zealand), giving it an added value in comparison to national systems: the states participating in ECHELON (UKUSA states) can place their interception systems at each other's disposal, share the cost and make joint use of the resulting information. This type of international cooperation is essential in particular for the worldwide interception of satellite communications, since only in this way is it possible to ensure in international communications that both sides of a dialogue can be intercepted. It is clear that, in view of its size, a satellite receiver station cannot be established on the territory of a state without that state's knowledge. Mutual agreement and proportionate cooperation among several states in different parts of the world is essential.