English summary: The religion of the Ancient Greeks has already been the subject of a whole series of introductions and syntheses whose usefulness is no longer in doubt. The present work differs from them by the reflection it offers on the plurality inherent in this religious system. Indeed, the tension between unity and plurality, between the general and the particular, is constitutive of the relations that the Greeks had with their many gods. Based on this observation, several questions run through the book: What is the relevance of the terms "religion" and "plurality"? Is there a "polytheism" to understand Ancient Greece? Should we speak of Greek religion in the singular or plural? Do divine figures dissolve in the variety of their cults to the point of becoming unrecognizable? Can we speak of "belief" in this context? Was the sacrificial practice strictly local or was it based on a background shared by all Greek communities? Taking Herodotus' Inquiry as a common thread, the investigation intends to do justice to a profusion of gods and rituals, carefully distinguishing between the fluid plurality of a complex system and the impression of chaos to which our own cultural determinisms risk reducing it. Vinciane Pirenne-Delforge (born 1963 in Belgium) teaches at the University of Liege and since 2017 has been the Professor of Religion, History and Society in the Ancient Greek World at the College de France. Her main fields of investigation are the ancient Greek religion -particularly its gods and ritual norms-, the functioning of ancient polytheistic systems and the historiography of religions. She has notably published L'Hera de Zeus. Ennemie intime, epouse definitive (2016) and, more recently, Le Polytheisme grec comme objet d'histoire (2018). French description: La religion des anciens Grecs fait regulierement l'objet d'introductions et de syntheses. Le present ouvrage s'en distingue par la reflexion qu'il propose sur la pluralite inherente a ce systeme religieux. En effet, la tension entre unite et pluralite, entre general et particulier est constitutive des relations que les Grecs entretenaient avec leurs nombreux dieux. A partir de ce constat, plusieurs questions traversent le livre. Quelle est la pertinence des termes de religion et de polytheisme pour comprendre la Grece antique ? Doit-on parler de religion grecque au singulier ou au pluriel ? Les figures divines se dissolvent-elles dans la variete de leurs cultes jusqu'a en devenir meconnaissables ? Peut-on parler de croyance dans ce cadre ? La pratique sacrificielle etait-elle strictement locale ou bien fondee sur un arriere-plan partage par toutes les communautes grecques ? En prenant l'Enquete d'Herodote comme fil rouge, l'investigation entend rendre justice a un foisonnement de dieux et de rituels, et rendre intelligible la pluralite fluide d'un systeme complexe, bien loin de l'impression de chaos a laquelle nos propres determinismes culturels risquent de le reduire.