Among children’s earliest spatial words are topological forms like ‘in’ and ‘on’. Although these forms name spatial relationships, they also presuppose a classification of ground objects into entities such as “containers” and “surfaces”; hence their relevance for a volume on “spatial entities”. Traditionally, researchers have assumed that semantic categories of space are universal, reflecting a human way of nonlinguistically perceiving and cognizing space. But, as this paper discusses, spatial categories in fact differ strikingly across languages, and children begin to home in on language-specific classifications extremely early, before age two. Learners do not, it seems, draw only on purely nonlinguistic spatial concepts; they can also actively construct spatial categories on the basis of the linguistic input. Evidence is drawn primarily from research on children learning Korean vs. English.