High-throughput technologies enable the study of various cellular systems — from subcellular systems such as signalling networks, multiprotein complexes and organelles to cells, tissues and even entire organisms. These systems can be modelled using a combination of high-throughput experimental data and computational and mathematical approaches, as illustrated in this month's Focus on Modelling Cellular Systems.

Information on the different signalling components and their interactions and properties is required for the modelling of signalling networks. On page 165, Boris N. Kholodenko describes how computational models can elucidate the spatial and temporal dynamics of signalling pathways. Large-scale signalling-component discovery and the reconstruction of signalling pathways can also be achieved through RNA-interference-mediated gene knockdown in mammalian systems, as reviewed by Jason Moffat and David M. Sabatini on page 177.

Moving from signalling networks to structure, Patrick Aloy and Robert B. Russell (page 188) explore how structural data can be used to turn rather abstract protein-interaction networks into more realistic models of protein interactions at atomic-level detail. High-resolution cryo-electron tomograms can extend such models by producing a complete whole-cell framework that can be used to create a proteome atlas, as described by Wolfgang Baumeister and colleagues on page 225.

These and other Focus articles will hopefully demystify the modelling approaches that can be used in cell biology. Finally, we would like to thank the sponsors of this Focus issue and accompanying Web Focus (http://www.nature.com/nrm/modelling) — Keio University, the Okinawa Institute of Science and Technology and the Systems Biology Institute (SBI).