Despite a growing interest for space in language, most research has focused on spatial markers specifying the static or dynamic relationships among entities (verbs, prepositions, postpositions, case markings…). Little attention has been paid to the very properties of spatial entities, their status in linguistic descriptions, and their implications for spatial cognition and its development in children. This topic is at the center of this book, that opens a new field by sketching some major theoretical and methodological directions for future research on spatial entities. It brings together linguistic descriptions of spatial systems, formal accounts of linguistic data, and experimental findings from psycholinguistic studies, all couched within a wide cross-linguistic perspective. Such an interdisciplinary approach provides a rich overview of the many questions that remain unanswered in relation to spatial entities, while also throwing a new light on previous research focusing on related topics concerning space and/or the relation between language and cognition.