The Canadian Security Intelligence Service (CSIS, /ˈsiːsɪs/; French: Service canadien du renseignement de sécurité, SCRS) is a foreign intelligence service and security agency of the federal government of Canada. It is responsible for gathering, processing, and analyzing national security information from around the world and conducting covert action within Canada and abroad. CSIS reports to the Minister of Public Safety and Emergency Preparedness, and is subject to review by the National Security and Intelligence Review Agency.

The CSIS has no law enforcement function and mainly focuses on intelligence gathering overseas. The agency is led by a director, the current being Daniel Rogers, who assumed the role on October 15, 2024.

Prior to 1984, security intelligence in Canada was the purview of the Royal Canadian Mounted Police (RCMP). However, during the 1970s, there were allegations that the RCMP Security Service – the predecessor to CSIS – had been involved in numerous illegal activities. As a result of these allegations, Justice David McDonald was appointed in 1977 to investigate the activities of the RCMP Security Service. The resulting investigation, known as the McDonald Commission, published its final report in 1981, with its main recommendation being that security intelligence work should be separated from policing, and that a civilian intelligence agency be created to take over from the RCMP Security Service.

On June 21, 1984, CSIS was created by an Act of Parliament. At the time, it was also decided that the activities of this new agency, the Canadian Security Intelligence Service, should be subject to both judicial approval for warrants and to general review by a new body, the Security Intelligence Review Committee, as well as the office of the Inspector General (which was disbanded in 2012). Its de facto existence began on July 16 under the direction of Thomas D'Arcy Finn. In its early years, its primary focus was on investigating terrorist groups in response to a number of violent crimes with political undertones, such as the bombing of an Air India jet departing from Montreal and the armed takeover of the Turkish embassy in Ottawa.

At first, the main emphasis of CSIS was combatting the activities of various foreign intelligence agencies operating in Canada. For example, it has been engaged in investigating economic espionage involving Chinese operations throughout Canada. While the threat posed by foreign intelligence agencies still remains, CSIS over the years since 9/11 has focused more and more on the threat to Canadian security and its citizens posed by terrorist activity, and this has led to the memorable cases of Maher Arar and Omar Khadr.

The institutional focus of CSIS returned to state actors (such as Russia and China) after a February 2021 speech by the CSIS director, David Vigneault, who warned that the Chinese "strategy for geopolitical advantage on all fronts — economic, technological, political and military" uses "all elements of state power to carry out activities that are a direct threat to our national security and sovereignty." Meanwhile, in May 2023, according to a CSIS intelligence assessment which provided an overview of Chinese government foreign interference in Canada, it was claimed that China sees Canada as a “high-priority target” and employs “incentives and punishment” as part of a vast influence network directed at legislators, business executives and diaspora communities.

In 2024, the Parliament of Canada passed the Countering Foreign Interference Act, which amended the Canadian Security Intelligence Service Act to give CSIS powers to investigate potential foreign interference in the Canadian political system.

The leadership position is mostly a political appointment.