How does “self-governance” happen in Wikipedia? Through in-depth interviews with eleven individuals who have held a variety of responsibilities in the English Wikipedia, we obtained rich descriptions of how various forces produce and regulate social structures on the site. Our analysis describes Wikipedia as an organization with highly refined policies, norms, and a technological architecture that supports organizational ideals of consensus building and discussion. We describe how governance in the site is becoming increasingly decentralized as the community grows and how this is predicted by theories of commons-based governance developed in offline contexts. The trend of decentralization is noticeable with respect to both content-related decision making processes and social structures that regulate user behavior.