A well-wrought cautionary tale about the dangers of trying to impose morality by law. Langum (Law/Samford Univ.; Law and Community on the Mexican California Frontier, not reviewed) traces the history of the Mann Act of 1910, which prohibited the transportation of women across state lines for ``prostitution or debauchery, or for any other immoral purpose.'' Under this law, people were arrested and imprisoned or fined simply for having sex out of wedlock after crossing into another state, or for asking someone to come visit in another state for the purpose of having pre- or extramarital sex. Those convicted became federal felons who were consequently unable to vote, closed out of jobs, denied naturalization. Langum shows how the law grew out of the early 20th century's ``white slavery'' scare, a mixture of antimodernism, racism, and an all but pathological fear of sexuality, as well as a frenzied response to immigration and urbanization. The author argues convincingly that, like Prohibition, which came in 1919, the Mann Act was a classic example of the Progressive movement's social engineering propensities and notes that it did not produce the effects Progressives desired; people didn't stop having sex outside of marriage, and prostitution didn't fade away. The white slavery hysteria abated (because it never existed), but the law left in its place a new opportunity for blackmail of unsuspecting men and a potential for new kinds of prosecutorial misconduct in the service of a ``morals crusade.'' The act was instrumental in the growth of the FBI and the rise of J. Edgar Hoover, and Langum thoroughly exposes Hoover's use of it as a club to beat suspected ``radicals'' like Charlie Chaplin. A trifle repetitive in a lawyerly way, but a thorough, often wryly funny, and closely argued work of legal and social history.