Systems biology is the study of biological systems whose behaviour cannot be reduced to the linear sum of their parts’ functions. Systems biology does not necessarily involve large numbers of components or vast datasets, as in genomics or connectomics, but often requires quantitative modelling methods borrowed from physics. Systems biology is the study of biological systems whose behaviour cannot be reduced to the linear sum of their parts’ functions. Systems biology does not necessarily involve large numbers of components or vast datasets, as in genomics or connectomics, but often requires quantitative modelling methods borrowed from physics. Biological systems are enormously complex, organised across several levels of hierarchy. At the core of this organisation is the genome that contains information in a digital form to make thousands of different molecules and drive various biological processes. This genomic view of biology has been primarily ushered in by the human genome project. The development of sequencing and other high-throughput technologies that generate vast amounts of biological data has fuelled the development of new ways of hypothesis-driven research. Development of computational techniques for analysis of the large data, as well as for the modelling and simulation of the complex biological systems have followed as a logical consequence. Simulatable computational models of biological systems and processes form the cornerstone of the emerging science of systems biology.