The project consists in studying the arguments used by the Christian Churches (both Catholic and Protestant) to defend religious truths in contemporary Western societies, from the Enlightenment to the 21st century. This study mainly focuses on France, Italy, Germany, the United Kingdom and Spain, without refraining from occasionally taking advantage of US examples. The use of the word apologetics for describing a general system of response to the challenges of the times is quite recent (mid-nineteenth century/mid-twentieth century), and it allows to identify a specific period of reconfiguration of the relations between society and religion. The appearance of the word apologetics is largely prepared upstream, since Christian apologies changed at the turn of the 17th and 18th centuries, and its rarefaction and its exclusion from the ecclesiastical field since the mid-20th century is then the manifestation of a new reconfiguration. The understanding of these scansions allows to grasp, according a long term historical analysis, the evolutions or the tensions of the believing discourse in its relations to modernity. Such an investigation first requires to approach ecclesial discourse from within. This approach is based on an abundant body of sources. However, the project mainly aims at using this corpus as a mirror of the changes experienced by contemporary Western societies: essentially "reactive", that is to say first of all defensive, apologetics is primarily a confrontation with all the difficulties that arise from the progressive transformation of the status of beliefs in contemporary societies. From this point of observation, it is possible to note that the difficulties, the blocking points (the opposition with philosophy, the “exact” or “social” sciences, the evolution of mores, etc.), allow to draw up an inventory of the characteristics of modernity in its relations with the Christian religion.