Ten years ago, the 'Blue Brain Project' launched with the aim of producing a biologically accurate model of the brain by combining experimental data with powerful computer algorithms. Markram and collaborators now describe the project's first output: the digital reconstruction of the microcircuitry of a 0.29 mm3 volume of juvenile rat somatosensory cortex. Sparse, experimentally measured information on neuronal morphology, physiology and organization was integrated into the 'first draft' digital reconstruction, the biological validity of which was tested by assessing its ability to reproduce several in vitro and in vivo experimental findings.