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The first part of this introduction will present “naive theories” from a historical point of view. It will show that, starting with Piagetian logical classes and then categorization, we now consider how young children attribute an “essence” to objects in order to define their identity and their function (Wellman and Gelman, 1991). In the second part, the explanatory models for the origins and development of these theories will be considered for the field of matter, that is, biology, and for the field of physics, concerning natural phenomena. The educability of certain biological notions (plants as living organisms) and physical notions (the Earth’s roundness) will also be discussed in the third section. In the final section, the five contributions to this special issue, relating to theories of disease and death (by Florence Labrell), conceptions of food (by Jean-Pierre Thibaut), children’s knowledge of genetic heritability (by Andrzej Tarlowski), mechanisms of the water and rain cycle (by Mesut Sackès, Sinem Güçhan Özgül and Kerem Avci) and astronomy, concerning the day/night cycle and the shape of the Earth (by Valérie Frède) will be briefly presented.