In 2008, a Dutch member of parliament released a short anti-Islamic film entitled Fitna, which stirred a huge public controversy and provoked public condemnations around the world. In response to the film, hundreds of videos were uploaded on YouTube, mostly with the aim to provide a more positive representation of Islam, express support for the author and his views, or defend his freedom of speech. Drawing on interviews with YouTube users who posted the videos, this paper reflects on the capacity of the Internet to sustain cosmopolitan communication and examines how cosmopolitan attitudes and practices on-line differ depending on the participants' cultural and social background, especially their religious affiliations. Particular attention is paid to how the opportunities for cosmopolitan communication are shaped by the unequal distribution of cosmopolitan attitudes and practices among groups, and by global inequalities of power. In addressing these issues, the paper also engages with broader debates about cosmopolitanism, and argues for an understanding of cosmopolitanism as a quest for universalism, which remains anchored in the particular, but involves communication across difference, and requires openness to the possibility that the other is right.