The chapter argues that dominant theories of regional cooperation and integration share a bias towards taking states as the main drivers of regionalism and focusing on processes of formal institution-building at the regional level. Nevertheless, many theoretical approaches still travel across regions if their concepts and explanatory logics are broadened beyond the economic realm. Where they largely fail, however, is in explaining similarities and differences in institutional designs of regional organizations and in accounting for their effects. The last part of the chapter suggests that the governance concept may help theories of regional cooperation and integration to overcome their statist and formal institutionalist bias strengthening their explanatory power. Governance gives equal status to state and non-state actors and does not prioritize formal over informal institutions. It thereby provides a useful framework to systematically compare varieties of regionalism across time and space and explain their emergence, outcomes, and effects.