The living cell is a complex system of interacting processes. The properties of the agents that facilitate these processes, such as enzymes, transporters and receptors, must be tuned to each other if the system is to behave harmoniously. The present chapter describes how the regulatory design of cellular subsystems that makes this harmonious behaviour possible can be visualized on a graph that combines the so-called log–log rate characteristics of these subsystems. The tools that are needed to create and analyse these graphs are metabolic control analysis, supply-demand analysis, enzyme kinetics and computer simulation.