The American geographer Ellen Churchill Semple (1863–1932), famous for her work on environmental influence, is often framed as a mere disciple of the German geographer Friedrich Ratzel (1844–1904). Drawing on a reading of Semple's published and unpublished works as well as correspondence and diaries, this paper sheds new light on the two anthropogeographers' intellectual relationship, which was in fact one with benefits to both sides. Semple found in Ratzel's geography a detached and scientific language with which to reinterpret American history. He drew on her as an informant on issues of racial segregation in the United States. Although Semple remained loyal to his broader intellectual project after his death, she had begun, soon after they met, to develop her own brand of anthropogeography, freed from the ambivalences of his work. Her sharpened reformulation, which he had endorsed, would ultimately make anthropogeography an easier target for its critics.