The Department of National Defence, (French : Ministère de la Défense nationale) frequently referred to by its acronym DND, is the department within the government of Canada with responsibility for all matters concerning the defence of Canada. In addition to the civilian components of the department, this also includes Canada's military, known as the Canadian Forces, whose personnel make up approximately two thirds of the department.

DND is the largest federal department in terms of personnel/employees and budget; there are 65,000 members of the Canadian Forces regular force, 26,000 members of the Canadian Forces primary reserve force, and approximately 29,000 civilian DND support employees. The department's planned spending in Fiscal Year 2008-2009 is C$19.5 billion. In 2006, the government announced a C$17 billion spending program for capital projects.

Until a December 2003 reorganization of the federal government, DND was in charge of emergency preparedness and response in Canada, through the Office of Critical Infrastructure and Emergency Preparedness. DND also holds responsibility for the Communications Security Establishment which is an organization staffed by a mixture of civilian and military personnel.

DND is led by the Minister of National Defence and is headquartered at National Defence Headquarters (NDHQ) in Ottawa.