In an important and long-awaited sequel to his classic Transformation of American Law, 1780-1860 (1977), Horwitz tells how the Progressive movement--a program for political and economic as well as legal reform--transformed American legal thought from a search for impartial norms into a discipline that acknowledged the elasticity of its own rules and that borrowed the methodologies and some of the values of the social sciences. Horwitz describes the Progressive movement (and its progeny, the Legal Realism movement of the 1920's and 1930's) as an assault on ``classical legal thought''--the view that the law constitutes an impartial body of rules administered by neutral arbiters. The author argues that centralization of the American economy--with the accompanying problems of urbanization, immigration, industrialism, and polarization of economic classes--led to a gradual reexamination of classical legal thought, particularly the bias in legal orthodoxy against redistribution of wealth. Horwitz describes how economic and, ultimately, social changes brought about by WW I put irresistible pressure on courts and legal scholars to bring jurisprudential thought into closer touch with America's rapidly changing society. But, Horwitz explains, it was the Supreme Court's controversial decision in Lochner v. New York (1905)--which invalidated a maximum-hours law for bakers on the grounds that it unconstitutionally interfered with the freedom of contract--that truly catalyzed the attacks of Progressive legal scholars on the claim that law was a politically neutral science. Through a discussion of the evolution of thought in specialized legal fields and problems, and by offering short sketches about the thought of influential figures of the period like Oliver Wendell Holmes and Legal Realists Karl Llewellyn and Jerome Frank, Horwitz demonstrates that the effect of the new thinking on American law was pervasive and lasting. Finally, he argues persuasively that the Legal Realist tradition has had an extensive effect on the development of American law in the post-WW II period. An excellent and significant reexamination of the work and impact of the Progressive and Realist legal thinkers.