This paper presents a framework for modelling and robust control of linear systems based on a graph point of view. Basic concepts such as linearity, causality, stabilizability can be defined as properties of the graph of a system. Uncertainty is naturally thought of in terms of perturbations of the graph. Modelling and approximation are also fundamentally related to the graph of the system. Robustness will be quantified in the graph setting using the gap metric. Necessary and sufficient conditions for robustness will be explained geometrically in terms of the graphs of the plant and controller. A flexible structure design example will be discussed.