For the use of their holdings I wish to thank the British Museum, the School of Slavonic and East European Studies (University of London), the London School of Economics, the library of Columbia University, the New York Public Library, and the Internationaal Instituut voor Sociale Geschiedenis (Amsterdam). The Trotsky Archives, which were essential for this work, were used by permission of the Harvard College Library. For her historical judgement and tireless assistance in the writing, my greatest debt is to my wife. For his bibliographical research on Trotsky I am grateful to Louis Sinclair. The Canada Council and Imperial Oil Ltd. were most generous in their financial support of my research. Olga Crisp, Peter Wiles, Heinz Schurer, R. W. Davies, H. Gordon Skilling, Robert McNeal and Robert Fenn all provided encouragement at various phases of preparing the manuscript. All responsibility for errors of fact or interpretation is of course my own.