Volume 40 contains the letters of Marx and Engels from 1856 to 1959. They throw light on the further development of communist theory by Marx and Engels, on Marx’s progress in his economic research, their joint journalistic work for Das Volk and the New York Daily Tribune and their efforts to set up a working- class party. Many letters deal with Marx’s work in 1857-58 on a series of manuscripts that formed the first draft of Capital. The letters also give an idea of the studies Marx and Engels carried out in other fields, in particular of Engels’ work on military theory and military history in connection with the articles for the New American Cyclopaedia. The Appendix contains letters by Jenny Marx to Frederick Engels and to other people, most of them written at Marx’s request.