This research project assesses the relationship between the use of Facebook and the development of social movements throughout their life cycle by focusing on the case study of Popolo Viola. On 5th December, 2009, hundreds of thousands of Italian citizens took to the streets of Rome to say 'no' to the politics of Silvio Berlusconi's government and to ask for his resignation as Prime Minister. The demonstration was planned and organized, mainly on Facebook, by a group of bloggers. A single-issue protest rapidly evolved into a social movement, called 'Popolo Viola', 'Purple People'. The colour purple was chosen because it was not previously associated with any political movement, and as a word to the wise that the movement was not linked to any political party. New groups and pages arose on Facebook: apart from the page 'il Popolo Viola', which now had more than 460,000 members (data August, 2013), thousands of pages and groups were opened at a local level, both inside and outside Italy. Through the lenses of Social Movement Theory and the Critical Theory of Technology this study focuses on the role played by the use of Facebook in the development of the movement's organizational structure, the building of its collective identity, and its mobilization processes. The methodology adopted for this purpose includes both quantitative and qualitative methods: on the one hand, there is an analysis of membership data and interaction levels on the Popolo Viola Facebook page, and a survey; on the other hand, there are in-depth interviews with the Facebook page administrators, influential members and activists of the movement, and content analysis of the online conversations among activists. The findings of this research show how Facebook proved to be an efficient mobilizing structure for the social movement only on a short-term basis. After its initial success, the incompatibility between the commercial interests behind Facebook's design, and the ideology of Popolo Viola became manifest. Facebook failed to provide the movement with the necessary instruments in terms of a shared democratic management of its resources. The inability to manage Facebook pages and groups according to commonly agreed values promoted vertical power structures within the movement, contributing to controversial management of the Facebook page and to internal divisions which significantly hindered the potential of the anti-Berlusconi protest. Moreover, gradual changes in the Facebook code increasingly promoted top-down flows of communication which, in conjunction with controversial decisions in the moderation of discussions that were made by the page administrators, progressively decreased the plurality of voices within the movement's page, and hampered the formation of a strong collective identity. Facebook therefore proved to represent much more than a mere communication tool for Popolo Viola, playing a vital role in influencing the movement's structure, leadership, communication flows and collective identity. The rise and fall of Popolo Viola, with all its complexity, constitutes a useful case study of the evaluation of technology as a problematic force for social change. That said, this is not an issue which relates to the technology itself, but rather to the values and interests that drive the actors who are involved in this power struggle. Taking into account the relationships between culture, technology and capital, this study offers a balanced assessment of the dynamics which characterize the development of social movement protest on commercial Social Network Media.