The aim of the present book is twofold: to set forth the leading phases of the historic socialism, and to attempt a criticism and interpretation of the movement as a whole. In this edition the changes in the history are concerned chiefly with the revival of the International, which, since the Stuttgart Congress in 1907, may be regarded as an accomplished fact. I have made it no part of my plan to dwell on details. The interest and significance of the history of socialism will be found, not in its details and accidents, but in the development of its cardinal principles, which I have endeavoured to trace. Readers desirous of detail must be referred to the writings of the various socialists, or to works that treat of special phases of the movement. Yet I hope that the statement of the leading theories is sufficiently clear and adequate to enable the reader to form his own judgment of the highly controversial matters involved in the history of socialism. I may add that in every case my account is drawn from an extensive study of the sources. These sources I have given both in the text and in footnotes. For the more recent development of the subject, however, the material is derived from such a multitude of books, pamphlets, periodicals, and journals, as well as from personal inquiry and observation, that it has not been found practicable to indicate them.