I argue that the change that eventually resulted in a three-dimensional representation of molecules was led, not by theory, but by modellingüa kind of modelling invented, not primarily to express chemical theory, but rather as a new way of communicating a variety of messages. By manipulating tin boxes or tinkering with little spheres and toothpicks, chemists not only visualised their abstract theoretical notions but also impressively testified to the claim that they would build a new world out of new materials. For this purpose molecular models supplied the elements of a new symbolic and gestic language by which chemists conquered new spaces: material space in the form of new substances, notional space in the new stereochemistry, and social space by expressing professional claims to power. Though the use of these models remained epistemologically problematic, their social and cultural message was much more easily understood, and this predisposed younger chemists to accept their implicitly constructivist and three-dimensional approach. The active construction of space was not peculiar to chemistry, but part of a more comprehensive change in perceiving the world and making it oneüs own, an attitude present in cultural domains from pedagogy to architecture.