Since 2007, the official doctrine of the French Ministry of the Interior has continuously affirmed that video surveillance is a tool for the prevention, deterrence and elucidation of criminal acts. This article sets out to evaluate the effectiveness of video surveillance with regard to this promise. It is based on a long-term survey (2012-2017) carried out in three cities (one small, one medium and one very large) in the South of France, and on a methodology that is both quantitative and qualitative. It highlights the great weakness of the contribution of video surveillance to the fight against crime, both in terms of the a posteriori elucidation of cases and “live” detection by the operators who view the images. The survey also shows how and why these technological devices are gradually being diverted to other uses that are more profitable but partly concealed because they are less socially acceptable.