Section 3142(e) of the Bail Reform Act of 1984 authorizes pretrial detention. In 1986, Anthony Salerno, an alleged Mafia mobster, was arrested and charged with narcotics trafficking, labor racketeering, construction bid-rigging, extortion, gambling, and conspiracy to commit murder. At a pretrial hearing, Salerno was ordered to be held without bail until trial under Section 3142(e) on the grounds that he posed a danger to the community. At the time Salerno was ordered detained, no U.S. court of appeals had found preventive detention unconstitutional. Shortly after Salerno was ordered detained, the Second Circuit Court of Appeals ruled that Section 3142(e) as applied violated the fifth amendment. Salerno appealed his detention to the second circuit in 1986 and a divided panel ruled that Salerno had been unconstitutionally detained under Section 3142(e). Because six other circuit courts of appeals had found Section 3142(e) constitutional, the U.S. Supreme Court granted certiorari in the Salerno case in order to resolve the conflict among the circuit courts regarding the constitutionality of Section 3142(e). In 1987, the U.S. Supreme Court reversed the second circuit and upheld Salerno's detention and the constitutionality of Section 3142(e) by a vote of 6 to 3. The author provides details of the legislative process that created Section 3142(e) as well as case law dealing with preventive detention. He analyzes arguments made in support of and against the constitutionality of the statute. 422 footnotes.