The Author comments on the antagonism between liberalism/illiberalism to describe the evolution of the European construction. He is particularly interested in how the political decision-makers interpreted social movements. For this purpose, the case-law of the Court of Justice is called upon. Referring to the post-war period, the Author provides a brief history of the ideas and presents their trends and contradictions. The conclusion reached is that the European project, having started with the strict aim of economic liberalism, gradually moved towards the construction of a liberal society. The author acknowledges that this objective often gives way to illiberal impulses. However, liberty is the true seismograph of the values of this, sometimes troubled, evolution.