Borrowed from English common law, this clause was of great importance to the authors of the United States Consitution, as it shows up early in the document, in Article One, Section Nine articulating limitations on the legislative branch:
The Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it.
This power necessarily brings with it a great deal of controversy, of course, because one of the fundamental American freedoms is that of either being charged with a crime if enough evidence can be accumulated to present in court, or released from custody. Abraham Lincoln exercised this power during the American Civil War, giving as his reason the need to protect national security by holding suspected Confederate sympathizers and keeping them from contributing to the Southern war effort. More recently, debate has centered on the detention camp at Guatanamo Bay, Cuba, established by the Bush administration in 2002 as part of the so-called "War on Terror".