Crossing over the Line describes the folly of the Mann Act of 1910—a United States law which made travel from one state to another by a man and a woman with the intent of committing an immoral act a major crime. Spawned by a national wave of "white slave trade" hysteria, the Act was created by the Congress of the United States as a weapon against forced prostitution.

This book is the first history of the Mann Act's often bizarre career, from its passage to the amendment that finally laid it low. In David J. Langum's hands, the story of the Act becomes an entertaining cautionary tale about the folly of legislating private morality.

Langum recounts the colorful details of numerous court cases to show how enforcement of the Act mirrored changes in America's social attitudes. Federal prosecutors became masters in the selective use of the Act: against political opponents of the government, like Charlie Chaplin; against individuals who eluded other criminal charges, like the Capone mobster "Machine Gun" Jack McGurn; and against black men, like singer Chuck Berry and boxer Jack Johnson, who dared to consort with white women. The Act engendered a thriving blackmail industry and was used by women like Frank Lloyd Wright's wife to extort favorable divorce settlements.

"Crossing over the Line is a work of scholarship as wrought by a civil libertarian, and the text . . . sizzles with the passion of an ardent believer in real liberty under reasonable laws."—Jonathan Kirsch, Los Angeles Times