This thesis offers a detailed socio-historical exploration of the practice of molecular modelling in chemistry and allied disciplines. This exploration leads to observations and conclusions that are of relevance to the sociology of science in general and to the issue of representation in scientific practice, in particular. After a general introduction in chapter one, chapter two offers a review of the science studies' literature relevant to the topic, namely the literature on representation and on experimental practices in the sciences. The lack of sources dealing with the issue of physical modelling is highlighted. Chapter three, through specific cases studies, presents the argument that the circulation of structural concepts and accounts in chemistry has been historically associated with the circulation not only of graphical representations, but also of physical models. Implications of this argument for a semiotically-centred view of scientific practice are discussed. Chapter 4 discusses the role of models as a research tool. Through various historical cases, it shows how physical models have been central in the process of defining, exploring and intervening on the domain of molecular-structures as accessed through laboratory manipulations. The work of molecular modelling is presented in particular as the experimental articulation of structural constraints within clearly defined research settings. Chapters five and six analyse the development of three specific modelling systems from the late 1930s to the mid-1960s. These chapters show these developments as contingent processes based on the involvement of elite researchers and both private and public institutions. It shows in particular how these modelling systems were made relevant across individual research sites by providing not only a technical solution to the problem of assembling model structures, but also by incorporating specific structural constraints. Finally, it is argued that these systems are one of

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