In his preface to the second volume of Capital, Friedrich Engels vigorously defended Marx against the accusation that he had stolen his theory of surplus value from J. K. Rodbertus. This charge of plagiarism dated from the 1870s and had been made by both Rodbertus himself and by his disciple Rudolf Meyer.¹ Its rebuttal was a matter of some urgency. In the early 1880s the dominance of Marxist ideas within German Social Democracy (which had never been especially secure) was under attack from a powerful "Rodbertus movement" led by Meyer, which exercised a considerable attraction for socialist-inclined intellectuals and threatened to seduce the party into a policy of compromise with the Bismarckian state, just as Lassalle had done earlier.² Engels's disciple Karl Kautsky savaged Prussian state socialism in the course of his polemic with C. A. Schramm in Die Neue Zeit, and the Engels-Kautsky correspondence is full of references to Rodbertian intrigues.³