The detailed description in this section is mainly based on two sources:  and .
Echelon consists of several components. The first component are five stations that are distributed all over the world targeted to all important telecommunication satellites (Intelsats). A station in England is targeted against the Atlantic, Europe, and the Indian Ocean. Two stations in the U.S. intercept communications of North and South America and parts of the Pacific, and two more stations are located in Australia and New Zealand to ensure global interception.
The next component of Echelon intercepts a range of satellite communication not carried by Intelsat. At least five more stations exist in England, Australia, Canada, Germany, and Japan.
The final component of Echelon are stations that tap into land-based telecommunication systems. This covers both cables and microwave networks. One of these facilities, for example, is located in London and taps into most communication across the Atlantic based on land and sea cables.
The computers in each station are called Dictionaries. They are connected via highly encrypted communications with the headquarters of the five agencies. All messages intercepted by one of the Dictionaries is sent to one of the headquarter for further processing.
To handle the huge amount of messages sent each day, each agency maintains a list of categories of interest. For each category a number of keywords are selected. These keywords may include names of people, organizations or objects.
These lists of categories are sent to the Dictionary computers which filter the incoming messages according to them. Whenever a relevant message is found it is sent to the headquarter that defined the according category. Essentially, an agency only sees those messages that they wanted to have filtered for themselves. Other filtered messages, even if it's done on one of their own Dictionary computers, are not visible. If an agency wants to have access to data gathered by Echelon for another agency, they need to apply for that.
The software used for Echelon is built with products from Memex (), an American company.
The core of all products from Memex is called "Memex Information Engine" (MIE). MIE is essentially a library used for information retrieval and management. It has very powerful functions to collect, analyze, and compare data. Furthermore, sophisticated search tools are provided that produce accurate hit lists.
Further applications made with MIE include CRIMINT (Criminal Intelligence System), used, for example, by the London Metropolian Police Force or the Scottish Criminal Intelligence Office. This software is a data management system that allows fast data retrieving and referencing between old and current operational data.
Another system is called PATHFINDER. It is a system to analyze and filter huge amounts of data, made in particular for the American army.