Under the July Monarchy, the French shared the conviction that the prison system needed to be reformed, and public opinion was fascinated by the topic. Experts were infavor of American-inspired measures, particularly isolation for prisoners and the use of solitary confinement. However, despite large debates and a genuine will to act, no reform succeeded in passing both Houses. A study of the arguments put forward shows that the main reason lies in a cultural incompatibility between two nations: it was impossible to enact a reform imported from the USA. As a result, no law enforcing the confinement system in French penitenciaries was voted between 1830 and 1848, (only) because of the American origin of the reform.La France de la monarchie de...