The issue of openness/secrecy has not received adequate attention in current discussion on the public sphere. Drawing on ideas in critical theory, political sociology, and cultural sociology, this article explores the cultural and political dynamics involved in the public sphere in modern society vis-à-vis the practice of open/secret politics by the state. It argues that the media, due to their publicist quality, are situated at the interface between publicity and secrecy, which thereby allows for struggles over the boundary of state openness/secrecy in the public sphere. A theory of boundary politics is introduced that is contextualized in the relationship among state forms, the means of making power visible/invisible (media strategies), and symbolic as well as discursive practices in the public sphere. In explaining the dynamics of boundary politics over openness/secrecy, three ideal-types of boundary creation are conceptualized: open politics, secrecy, and leak. The theory is illustrated with a case study of the Patten controversy in Hong Kong.