This chapter discusses challenges to civil liberties that have occurred throughout American history in the name of national security. It covers civil liberty issues during the Early Republic and Civil War, including the Alien and Sedition Acts and suspension of habeas corpus. It also discusses the Red Scares of the 20th century and the internment of Japanese Americans during World War II. The chapter then examines ongoing debates around balancing civil liberties with government responses to terrorism, including issues like surveillance, profiling, detention policies, extraordinary rendition, and torture.