This Practice Note discusses the national security review of investments under the Investment Canada Act, R.S.C. 1985, c. 28 (1st Supp.). It looks at what constitutes a national security review and the criteria relevant to a determination that an investment is “injurious to national security”. It also looks at the process, timelines, and information required for a national security review. It concludes by looking at key transactions that raised national security concerns under the Investment Canada Act.