This chapter presents a new, annotated translation of the famous treatise Airs, Waters, and Places (c. late 5th century BC), attributed, perhaps incorrectly, to the medical writer Hippokrates of Kos. The treatise sets out a model of how environment and seasonal conditions promote specific physiological conditions in the human body, and assesses the relationship between nature and custom as determinants of the physiology, ethical character, and social organization of Asian peoples, focusing on a comparison between European and Asian Skythians. A final passage identifies the greater variability among Europeans. The chapter introduction suggests a nuanced view of the controversial closing pages of the work: the author does not consistently regard Europeans as superior, but–perhaps under the influence of Athenian power–emphasizes the importance of understanding political systems.