The Communications Security Establishment (CSE; French: Centre de la sécurité des télécommunications, CST), formerly (from 2008-2014) called the Communications Security Establishment Canada (CSEC), is the Government of Canada's national cryptologic agency. It is responsible for foreign signals intelligence (SIGINT) and communications security (COMSEC), protecting federal government electronic information and communication networks, and is the technical authority for cyber security and information assurance.

Administered under the Department of National Defence (DND), the CSE is accountable to the Minister of National Defence through its deputy head, the Chief of CSE. The National Defence Minister is in turn accountable to the Cabinet and Parliament. The current Chief of the CSE is Caroline Xavier, who assumed the office on 31 August 2022.

In 2015, the agency built a new headquarters and campus encompassing 340,000 m² (84 acres). The facility totals a little over 110,000 m² (1,200,000 sq ft) and is adjacent to CSIS.