Here’s what you should know about the partnership that has been described as the “Five Eyes,” the “world’s most exclusive intelligence sharing club”:

1. The Five Eyes (FVEY) is an intelligence community consisting of Australia, Canada, the United Kingdom, the United States, and New Zealand. The FVEY group is a cooperative, complex network of linked autonomous intelligence agencies from each of these countries.

2. The FVEY partnership began with the UKUSA agreement, first called the BRUSA Agreement. This agreement, signed in March 1946 and still in effect, was the basis for cooperation in signals intelligence between the two nations. The agreement was later extended to include former British Dominions—Canada in 1948 and Australia and New Zealand in 1956.

3. For most of FVEY’s existence, the details about the existence of the arrangement have been kept strictly confidential. The partnership was so secret that Australian prime ministers were reportedly unaware of its existence—or their country’s involvement—until 1973. The program was also not acknowledged by the U.S. or UK until 2010 when both countries declassified documents relating to the partnership.

4. The group got its name from the way intelligence products are classified. For example, a Top Secret document intended only for Canadian intel officials, explains James Cox, would be stamped as, “TOP SECRET—CANADIAN EYES ONLY.” Intelligence products to be shared with the group of closest intelligence allies are marked “SECRET— AUS/CAN/NZ/UK/US EYES ONLY.” According to Cox, in conversation allied intelligence personnel adopted the term “Five Eyes” as a form of verbal shorthand because it was easier to say than “AUS/CAN/NZ/UK/US.”

5. The FVEY partnership focuses on the subset of intelligence collection known as signals intelligence (SIGINT). SIGINT is a category of intelligence comprising all communications intelligence, electronic intelligence, and foreign instrumentation signals intelligence, however transmitted.

6. The agencies within FVEY have a uniquely open and close relationship. As one senior member of Britain’s intelligence community has said:

When you get a GCHQ [UK’s SIGINT organization] pass it gives you access to the NSA too. You can walk into the NSA and find GCHQ staff holding senior management positions, and vice versa. When the NSA has a piece of intelligence, it will very often ask GCHQ for a second opinion. There have been ups and downs over the years, of course. But in general, the NSA and GCHQ are extremely close allies. They rely on each other.

And as Richard J. Aldrich says, “Sharing in this realm [SIGINT] between the United States, the UK, Australia and Canada is so complete that national product is often indistinguishable.”

7. During the Cold War, the FVEY partners reportedly developed a global communications monitoring program known as ECHELON. The program is said to have used ground-based signal stations located around the world to collect Soviet satellite communications. Since then, the program is claimed to have developed the ability to monitor emails, fax, telephone, and Internet communications. ECHELON is believed to capture all communication traffic and sift through it for keywords or other suspicious activity.

8. The original UKSUSA agreement “evolved into a common understanding that both governments will not target each other’s citizens/persons.” However, a 2005 draft of an NSA directive says the partners “reserved the right to conduct intelligence operations against each other’s citizens “when it is in the best interests of each nation.”

9. Last year Canada announced it would temporarily stop sharing metadata with FVEY partners because the Communications Security Establishment (CSE)—Canada’s equivalent of the NSA—“did not properly minimize Canadian identity information contained in certain metadata prior to being shared.”

10. In addition to the Five Eyes alliance, a number of other surveillance partnerships exist, such as: 9 Eyes: the Five Eyes, with the addition of Denmark, France, the Netherlands, and Norway; 14 Eyes: the 9 Eyes, with the addition of Germany, Belgium, Italy, Spain, and Sweden; and 41 Eyes: all of the these countries, with the addition of the allied coalition in Afghanistan.

Joe Carter is an adjunct professor of journalism at Patrick Henry College, an editor for several organizations, and the author of the NIV Lifehacks Bible.

Photo Credit: An aerial image of the Government Communications Headquarters (GCHQ) in Cheltenham, Gloucestershire. GCHQ is one of the three UK Intelligence Agencies and forms a crucial part of the UK’s National Intelligence and Security machinery. Source: Defence Images, via Flickr.