A M MONG historians of Latin America, Frank Tannenbaum enjoys the reputation of a pioneer, especially in two areas. His monograph The Mexican Agrarian Revolution (1929) was the first systematic and detailed treatment of the Mexican agrarian system and the policies designed to reform it. His subsequent two books on Mexico, Peace by Revolution (1933) and Mexico: The Struggle for Peace and Bread (1950) established Tannenbaum as the first major foreign interpreter of the Revolution of 1910. In quite a different area, Tannenbaum's seminal essay of 1946, Slave and Citizen: The Negro in the Americas, initiated the comparative study of slave systems. His work in both areas has been highly controversial, periodically attacked and vindicated, but rarely dismissed. Despite Tannenbaum's reputation and his position as a teacher of Latin American history at Columbia University for almost three decades, he was primarily neither a historian nor a Latin Americanist. Of his 15 books, only 7 deal exclusively with Latin America, and perhaps only one is distinctly historical. Tannenbaum's doctoral degree was in economics. Lewis Hanke once identified him as a political scientist. Closer to the mark, his lifelong friend and colleague, John Hermann Randall, called him a social philosopher. Tannenbaum himself considered his greatest accomplishment to be the establishment of Columbia's University Seminars, which were not only interdisciplinary but interoccupational and only tangentially concerned