This chapter examines the role of divination in classical Greek military decision-making. Focusing on divination by sacrifice in the works of Xenophon, and drawing on a range of anthropological studies of contemporary divination, it argues that divination, far from being an irrational intrusion into otherwise rational planning, was instead an important thinking tool for Greek commanders, helping them to crystallise hunches and intuitions about fluid and partially known tactical situations and formulate plausible plans for action. Divination is thus characterised as a process of active sense-making that is intensely practical in its focus.