Within five years Wikipedia has become an increasingly visible resource for information searches on the Internet. Audience ratings show it to be one of the main media based on participant publics. This article examines its emergence and historical context, situating it in the ecology of participative Internet. The author uses statistical data to consider the character of Wikipedia as a medium, and explores the main mechanisms of regulation (attribution of technical functionalities to the participants, implementation of control devices, and rules and procedures applied to coordination). Finally, the testing of these mechanisms in the construction of articles is analysed, revealing the uncertain nature of their embeddedness in this media device.