In the ancient Greece of Pericles and Plato, the polis, or city-state, reigned supreme, but by the time of Alexander, nearly half of the mainland Greek city-states had surrendered part of their autonomy to join the larger political entities called koina. In the first book in fifty years to tackle the rise of these so-called Greek federal states, Emily Mackil charts a complex, fascinating map of how shared religious practices and long-standing economic interactions faciliated political cooperation and the emergence of a new kind of state. Mackil provides a detailed historical narrative spanning five centuries to contextualize her analyses, which focus on the three best-attested areas of mainland Greece―Boiotia, Achaia, and Aitolia. The analysis is supported by a dossier of Greek inscriptions, each text accompanied by an English translation and commentary.