The notion of imitation occupies a central place in the thinking of sociologists, historians and art historians. After examining several theoretical approaches, the author proposes to distinguish two modalities of imitation: one idealist (the imitation of an ideal model), the other objectivist (that of a material object). Medieval vocabulary traditionally hears the words imitatio or imitari in a rather idealistic sense, for example in sacramental theology (the mass as imitation of the Passion), in the typological tradition of “the figurative interpretation of reality” (Erich Auerbach) or in Christian spirituality (the Imitation of Jesus Christ by Thomas a Kempis). But between the thirteenth and the beginning of the fifteenth century, the “objectivist” conception of imitation progressed by focusing on the singularity of observable and imitable material realities. This development concerns innovations in the plastic arts (Villard de Honnecourt), the rise of the likeness of portraiture, the birth of landscape painting, the success of the “mystery” theater. It benefits from the rediscovery of Aristotle’s Physica, but above all results from a cultural mutation of much greater magnitude: a transformation of Western ontology by the gradual passage from medieval analogism to modern naturalism (Ph. Descola).