The best-known controversies over Darwinian theory took place in public or in printed reviews. Many of these were highly polemical, presenting an over-simplified picture of the disputes. Letters, however, show that the responses to Darwin were extremely variable. Many of his strongest public supporters, such as Thomas Henry Huxley, Joseph Dalton Hooker, and Asa Gray, continued to have sharp theoretical differences with him; on the other hand, a number of his public critics assisted his research privately. Correspondence was itself an important arena of debate, one that Darwin greatly preferred to the public sphere. Often sharp disagreements could be resolved or overcome, and friendship and support sustained in spite of enduring differences. Darwin’s correspondence can thus help broaden our understanding of the role of scientific controversy and the ways in which it was conducted in the nineteenth century.