Any signalling network must be able to extract weak signals from a noisy environment and be robust against background perturbations, such as stochastic fluctuations in protein levels or variations in temperature and ambient stimulation. Our aim is to elucidate how these tasks have been solved in the evolutionary design of the chemotaxis pathway in E. coli, one of the best studied models for signal transduction. Combining fluorescence-based experimental analyses of spatial and temporal dynamics of the intracellular signal processing with quantitative computer modelling, we show that the robustness of chemotactic signalling is ensured at multiple levels, from gene expression to pathway topology to reaction rates.