UKUSA Agreement in the context of "1943 BRUSA Agreement"

Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of signals, whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). As classified and sensitive information is usually encrypted, signals intelligence may necessarily involve cryptanalysis (to decipher the messages). Traffic analysis—the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis.

The Five Eyes (FVEY) is an Anglosphere intelligence alliance comprising Australia, Canada, New Zealand, the United Kingdom, and the United States. These countries are party to the multilateral UKUSA Agreement, a treaty for joint cooperation in signals intelligence. Informally, "Five Eyes" can refer to the group of intelligence agencies of these countries. The term "Five Eyes" originated as shorthand for a "AUS/CAN/NZ/UK/US Eyes Only" (AUSCANNZUKUS) releasability caveat.

The origins of the FVEY can be traced to informal, secret meetings during World War II between British and American code-breakers that took place before the US formally entered the war. The alliance was formalized in the post-war era by the UKUSA Agreement in 1946. As the Cold War deepened, the intelligence sharing arrangement was formalised under the ECHELON surveillance system in the 1960s. This system was developed by the FVEY to monitor the communications of the Soviet Union and Eastern Bloc; it is now used to monitor communications worldwide. The FVEY expanded its surveillance capabilities during the course of the "war on terror", with much emphasis placed on monitoring the Internet. The alliance has grown into a robust global surveillance mechanism, adapting to new domains such as international terrorism, cyberattacks, and contemporary regional conflicts.

ECHELON, originally a secret government code name, is a surveillance program (signals intelligence/SIGINT collection and analysis network) operated by the five signatory states to the UKUSA Security Agreement: Australia, Canada, New Zealand, the UK and the United States, also known as the Five Eyes.

Created in the late 1960s to monitor the military and diplomatic communications of the Soviet Union and its Eastern Bloc allies during the Cold War, the ECHELON project became formally established in 1971. By the end of the 20th century, it had greatly expanded.

During the 2010s, international media reports revealed new operational details about the Anglophone cryptographic agencies' global surveillance of both foreign and domestic nationals. The reports mostly relate to top secret documents leaked by ex-NSA contractor Edward Snowden. The documents consist of intelligence files relating to the U.S. and other Five Eyes countries. In June 2013, the first of Snowden's documents were published, with further selected documents released to various news outlets through the year.

These media reports disclosed several secret treaties signed by members of the UKUSA community in their efforts to implement global surveillance. For example, Der Spiegel revealed how the German Federal Intelligence Service (German: Bundesnachrichtendienst; BND) transfers "massive amounts of intercepted data to the NSA", while Swedish Television revealed the National Defence Radio Establishment (FRA) provided the NSA with data from its cable collection, under a secret agreement signed in 1954 for bilateral cooperation on surveillance. Other security and intelligence agencies involved in the practice of global surveillance include those in Australia (ASD), Britain (GCHQ), Canada (CSE), Denmark (PET), France (DGSE), Germany (BND), Italy (AISE), the Netherlands (AIVD), Norway (NIS), Spain (CNI), Switzerland (NDB), Singapore (SID) as well as Israel (ISNU), which receives raw, unfiltered data of U.S. citizens from the NSA.