More than half of these letters appear in English for the first time. They reflect the problems in the consolidation of the socialist parties and the formation of the 2nd International.

Engels continued to devote much time to the preparation of new editions and translations of his own and Marx's works. A number of letters elucidate key Marxist propositions, and defend them against simplistic interpretations and distortions. They present the essence of the Marxist method of analyzing the historical process. Questions of how to structure and build the working-class party, of democracy in the party, and opposition to sectarian or dogmatic views loom large. We follow Engels' taking an active part in consolidating the labor and socialist movements in Europe and the USA, and promoting international socialist ties.