Is the Internet a boon or a threat to democratic debate? Is it a lever for the Balkanization of political opinion or the ferment of new deliberative practices? This article presents a synthesis of research on the subject. The author notes that this issue was discussed in the early days of the Internet, through the experience of on-line communities, and should be placed in the context of media research. On-line forums are examined through the study of major national political debates in France and the US, and in the framework of Internet use in political engagement.