Human brain contains 86 billion neurons and trillion synapses per cubic centimeter cortex. Human brain poorly understood due to scarce high-quality postmortem tissue. Only 40-50 control brains available yearly in largest US brain bank. Allen Human Brain Atlas maps gene expression across all genes and structures in multiple entire brains. Includes microarray data from 500 anatomic regions per hemisphere in three brains. Provides over 100 million microarray data points and 46,000 ISH images. 84% of human genes expressed somewhere in brain. MRI and DTI imaging for all brains used. ISH studies cover schizophrenia, autism, subcortex, cortex, neurotransmitters. Data reveals 79% gene expression similarity between mouse and human visual cortex. Atlas prioritizes GWAS candidate genes for brain diseases. Enables translation of mouse brain findings to humans. Supports prediction of gene-phenotype associations like seizure susceptibility. Free online tools include 3D viewer, heatmaps, gene searches. Used by 7,000 unique visitors monthly worldwide.