Trotsky's contribution to historical materialism has been subject to two broadly defined critical assessments. Detractors have tended to dismiss his interpretation of Marxism as a form of productive force determinism, while admirers have tended to defend his Marxism as a voluntarist negation of the same. In this essay I argue that both of these opinions share an equally caricatured interpretation of Second International Marxism against which Trotsky is compared. By contrast, I argue that Trotsky's Marxism can best be understood as a powerful application and deepening of the strongest elements of Second International methodology to a novel set of problems. Thus, against Trotsky's admirers, I locate his Marxism as both emerging out of, in addition to breaking with, Second International Marxism; while, against his critics, I argue that it was precisely the strengths of this earlier interpretation of Marxism that informed Trotsky's powerful contributions to historical materialism: his concept of combined and uneven development and his discussion of the role of individual agents within the Marxist interpretation of history.