This study addresses the neglected subject of hetaireia (roughly, “warrior-companionship”) in Homer. Although many discussions of Homer mention hetairoi in passing, no study treats semantic, poetic, social, and military aspects comprehensively. The purpose of this dissertation is to fill this gap. To this end I explicate the meaning of the heta(i)r- root, survey the social and military roles of Homeric hetairoi, and expose the way the Iliad and the Odyssey use hetaireia to portray pathos and character. The argument is informed by the etymology of heta(i)r- from the PIE reflexive *swe-, but rests on a catalogue and analysis of all scenes in which hetairoi appear. The four chapters of this dissertation argue that hetaireia is a major axis on which both epics turn. The two chapters on the Iliad show what the world is like when hetaireia dominates and consider how a poem about war focuses on the bond between warriors and their companions. The two chapters on the Odyssey show how the world changes when hetaireia disappears and consider how a poem about homecoming replaces the relationships of the battlefield with the relationship between the oikos and the gods. A brief concluding chapter suggests how the analysis of hetaireia presented in this dissertation might affect Homeric studies, cultural, social, and military history of the archaic period, ancient philosophy, the history of psychology, and aspects of modern military psychology, particularly leadership and motivation in battle.