It was the first civilian office in Canada solely dedicated to decryption of communications signals; until then, SIGINT was entirely within the purview of the Canadian military, and mostly limited to intercepts.

[9] In March 1942, XU moved next door to Laurier House in Sandy Hill, Ottawa;[10] this location was chosen because they felt it would draw no suspicion to the enemies.

[9] In September 1945, U.S. President Harry Truman declared it would be vital to carry out such operations, and Canadian authorities came to the same conclusion in December later that year.

[9] With Edward Drake as its first director, the agency worked with intercepted foreign electronic communications, collected largely from the Royal Canadian Signal Corps (RCCS) station at Rockcliffe Airport in Ottawa.

[13] This unit successfully decrypted, translated, and analyzed these foreign signals, and turned that raw information into useful intelligence reports during the course of the war.

[10] During the Cold War, the CBNRC was primarily responsible for providing SIGINT data to the Department of National Defence regarding the military operations of the Soviet Union.

[10] CBNRC and the information it gathered and shared was kept secret for 34 years until 9 January 1974, when CBC Television aired a documentary titled The Fifth Estate: The Espionage Establishment.

[19] As part of the omnibus bill, oversight of CSE activities was assumed by the newly created National Security and Intelligence Review Agency (NSIRA).

However, CSE is one of several federal departments and agencies (primarily those having law enforcement, security or regulatory functions) that have been granted a badge by the Canadian Heraldic Authority.

[14] During the Cold War, CSE's primary client for signals intelligence was National Defence, and its focus was the military operations of the then Soviet Union.

Since the end of the Cold War, Government of Canada requirements have evolved to include a wide variety of political, defence, and security issues of interest to a much broader range of client departments.

[9] Officially created on 1 October 2018, CCCS consolidated the existing operational cyber-security units of several federal government organizations, including Public Safety Canada's Canadian Cyber Incident Response Centre, Shared Services Canada's Security Operations Centre, and the CSE's Information Technology Security branch.

[24][25] Formerly known as communications security (COMSEC), the CSE's Information Technology Security branch grew out of a need to protect sensitive information transmitted by various agencies of the government, especially the Department of Foreign Affairs and International Trade (DFAIT), Canada Border Services Agency (CBSA), DND, and the Royal Canadian Mounted Police (RCMP).

[27] Officially created on 1 October 2018, CCCS consolidated the existing operational cyber-security units of several federal government organizations, including the Canadian Cyber Incident Response Centre of Public Safety Canada; the Security Operations Centre of Shared Services Canada; and the Information Technology Security branch of CSE.

[30][29] Named after cryptanalyst and mathematician William T. Tutte, TIMC is based within CSE's Edward Drake Building in Ottawa.

[31] Researchers Leland McInnes and John Healy at the Tutte Institute developed a technique called Uniform Manifold Approximation and Projection (UMAP), originally designed to analyze malware.

A new CA$1.2 billion[33] facility, encompassing 72,000 square metres (18 acres), has been built in the eastern part of Ottawa, immediately west of the headquarters building for the Canadian Security Intelligence Service.

In the 2007 Proceedings of the Canadian Senate Standing Committee on National Security and Defence, then-CSE Chief John Adams indicated that the CSE is collecting communications data when he suggested that the legislation was not perfect in regard to interception of information relating to the "envelope.

(After the September 11 attacks on the United States in 2001, however, CSE's powers expanded to allow the interception of foreign communications that begin or end in Canada, as long as the other party is outside the border and ministerial authorization is issued specifically for this case and purpose.

[37] As with any other federal department or agency of Canada, the activities of CSE are also subject to review by various federal bodies, including:[37] Oversight over CSE was formerly provided by the Office of the Communications Security Establishment Commissioner (OCSEC; French: Bureau du commissaire du Centre de la sécurité des télécommunications, BCCST), which was created on 19 June 1996 to review CSE's activities for compliance with the applicable legislation, accept and investigate complaints regarding the lawfulness of the agency's activities, and to perform special duties under the 'Public Interest Defence' clause of the Security of Information Act.

Its capabilities are suspected to include the ability to monitor a large proportion of the world's transmitted civilian telephone, fax and data traffic.

"[43] CBNRC and the information it gathered and shared was kept secret for 34 years until 9 January 1974, when the CBC Television documentary show, The Fifth Estate, aired an episode focused on the organization, with research by James Dubro.

[16] A former employee of the organization, Mike Frost, claimed in a 1994 book, Spyworld, that the agency eavesdropped on Margaret Trudeau to find out if she smoked marijuana and that CSE had monitored two of former British prime minister Margaret Thatcher's dissenting cabinet ministers in London on behalf of the UK's secret service.

[45] In 2006, CTV Montreal's program On Your Side conducted a three-part documentary on CSE naming it "Canada's most secretive spy agency" and that "this ultra-secret agency has now become very powerful," conducting surveillance by monitoring phone calls, e-mails, chat groups, radio, microwave, and satellite.

[47] In 2013, a coalition of civil liberties associations launched a campaign directed against the government's perceived lack of transparency on issues related to the agency, demanding more information on its purported domestic surveillance activities.

[49] In 2014, a leaked, top-secret presentation entitled “IP Profiling Analytics & Mission Impacts” summarized experiments tracking the cellphones of travellers passing through Toronto Pearson International Airport.