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 a science-based discipline that aspires to study a biological system at various levels in its entirety, ranging from cell networks to cells and complete organisms. It involves the mapping of pathways, gene and protein interactions and logical ‘circuitry’ of natural organisms at the cellular, tissue and whole-organism level and the integration of this information into a computer model. Its primary goal is to attain a quantitative and predictive understanding of a biological system.