Today we live a true counterrevolution. Since the 1980s, in fact, the richest have continued to increase their share of income and wealth, reversing the earlier secular trend to reducing wealth gaps. The economic and social factors that engendered this situation are well known. But the deterioration of the idea of ​​equality also played a crucial role in leading insidiously to delegitimizing tax and redistribution actions. On the other hand, the denunciation of inequalities experienced as unacceptable today has a form of resignation and a feeling of impotence. Consequently, there is nothing more urgent than to refound the idea of ​​equality to get out of the impasses of our time. The book contributes to this company in a double way. In remaking the history of the two centuries of debates and struggles on the question, in the first place illuminates in an unprecedented way the current situation. He then elaborates a philosophy of equality as a social relation that allows us to go beyond the theories of justice that John Rawls and Amartya Sen have so far dominated contemporary reflection. And it shows that the reconstruction of a society based on the principles of singularity, reciprocity and communality is the condition of a more active solidarity.