The Canadian Security Intelligence Service (CSIS, ; French: Service canadien du renseignement de sécurité, SCRS) is Canada's primary national intelligence agency. It is responsible for collecting, analysing, reporting and disseminating intelligence on threats to Canada's national security, and conducting operations, covert and overt, within Canada and abroad. The agency also reports to and advises the minister of public safety on national security issues and situations that threaten the security of the nation.

CSIS is headquartered in Ottawa, Ontario, in a purpose-built facility completed in 1995. The agency is responsible to Parliament through the minister of public safety, and it is overseen by the National Security and Intelligence Review Agency. CSIS is also subject to review by the Federal Court. CSIS agents are not allowed to make arrests.

The agency is led by a director, the ninth and current being David Vigneault, who assumed the role on June 19, 2017.