The fundamental purpose of this book is to investigate the genetic moment of the concept of secularism and to examine the role of non-legal intellectual debate in the process of formation and development of this concept, with particular reference to a specific cultural context - the French one - in a determined period of time - the analysis spans from 1850 to 2023 - in order to verify whether and how literary components have contributed to determining its meaning and playing a role in its evolution in the French national legal system and in the process of overflowing into other legal systems in which it has been a protagonist. The underlying idea of this investigation is that a legal tradition is not composed only of a set of laws and regulations, but also of a set of deeply rooted attitudes and beliefs, which are influenced by history and intellectual debate: this perspective places a legal system as an integral part of the culture to which it belongs, and also underlines the importance of the socio-cultural context in understanding the definition, nature, and function of legal concepts within a given normative system.