This dissertation is a study of the economic history of the Hellenistic Achaian koinon, elucidating the ways in which federal structures impacted economic activity in the ancient Greek world and nuancing the analysis of Hellenistic economic history by moving beyond the polis-kingdom dichotomy that has dominated much recent research. It examines both structural factors that would have impacted economic activity, including environment, infrastructure, local cultures, and federal mechanisms, and to what extent these factors actually impacted economic activity. This involves the analysis of datasets from various subdisciplines, including literature, epigraphy, numismatics, ceramic studies, and survey archaeology, in order to evaluate and counterbalance the written sources that have dominated traditional studies of the Achaian koinon. The theoretical approach of New Institutional Economics is employed as a heuristic framework throughout. As a result of its imposition of more robust and expansive legal frameworks, standardized metrological instruments, and a relatively homogeneous monetary system, the Achaian koinon expanded property rights, allowed for greater enforcement of contracts, and reduced transaction costs across a large swathe of southern Greece and beyond. With the reduction of institutional barriers to economic activity, markets both within the koinon and without, in particular the Boiotian and Aitolian koina as well as Athens, would have become increasingly integrated. But while federal politicians were intent on facilitating broader economic exchange in order to ensure that essential goods and services were available to member communities, their material interests led them to limit the intervention of the federal government in issues of economic inequality, especially with respect to the more equitable redistribution of resources. This was especially relevant because embedded forces impelled the consolidation of land holdings in the hands of a relatively small supra-civic elite as the koinon expanded. Furthermore, its physical and governmental structures benefited economically the poleis of Achaia, the northeast, and Arkadia over the rest of the Peloponnese by directing government resources directly to them; by spurring the regular movement of groups to these regions; and by allowing them to mint freely within its decentralized monetary system.