Abstract The article addresses the main theory of the political public sphere generally, and the role of the Internet and Internet‐based media in the theory specifically. It first reviews briefly the initial social research on the Internet in the 1990s concerning political participation. After a presentation of Jürgen Habermas' theory of the contemporary public sphere, it proceeds to discuss the main problems concerning the Internet as a platform or infrastructure for public debate: segmentation and concentration. It argues that a general conclusion is that the public sphere differentiates and become more complex. A key task for future research, it argues, is to investigate the complex connections between Internet publics and mass media publics.