This paper first provides a historical overview of Internet use in French and American electoral campaigns. It then studies political practices on social networking sites such as Facebook, Twitter and Pinterest in the 2012 U.S. and French electoral campaigns. The reasons for the adoption of social networks by campaign teams are discussed and interpreted. Two case studies show the importance of public controversies, of the blurred boundaries between public and private lives as well as of the need for politicians to display grass roots participation in politics.