Gene networks have proven their utility for elucidating transcriptome structure in the brain, yielding numerous biological insights. Most analyses have focused on expression relationships within a circumspect number of regions -how these relationships vary across a broad array of brain regions is largely unknown. By leveraging RNAsequencing in 864 samples representing 12 brain regions in a cohort of 131 phenotypically normal individuals, we identify 12 brain-wide, 114 region-specific, and 50 cross-regional co-expression modules. We replicate the majority (81%) of modules in regional microarray datasets. Nearly 40% of expressed genes fall into brain-wide modules corresponding to major cell classes and conserved biological processes.Region-specific modules comprise 25% of expressed genes and correspond to regionspecific cell types and processes, such as oxytocin signaling in the hypothalamus, or addiction pathways in the nucleus accumbens. We further leverage these modules to capture cell-type-specific lncRNA and gene isoforms, both of which contribute substantially to regional synaptic diversity. We identify enrichment of neuropsychiatric disease risk variants in brain wide and multi-regional modules, consistent with their broad impact on cell classes, and highlight specific roles in neuronal proliferation and activity-dependent processes. Finally, we examine the manner in which gene coexpression and gene regulatory networks reflect genetic risk, including the recently framed omnigenic model of disease architecture.Using this hierarchy, we form a tree of consensus co-expression networks for each split, thereby generating co-expression modules for 20 hierarchical expression categories: 12 brain region specific categories (corresponding to each sampled region), 7 multiregional categories (corresponding to multiple, structurally-linked regions, figure 1b), and a brain-wide category. The majority of the resulting modules are highly overlapping, therefore we group these modules hierarchically into groups of highly similar modules which we term "module sets" (Methods). In total, we identify 311 modules at all levels, of which 173/199 (87%) of the tissue-level modules are replicated with strong support in at least one other independent dataset (figure 1c; Methods). Finally, by using network preservation statistics on all samples within regions and meta regions, we verify that module sets are supported by strong evidence within their own regions and little evidence outside of them (figure 1d).To test whether co-expression modules vary substantially by the method used for co-expression network construction, we build modules at the tissue level using three alternative approaches: ARACNe, 34 PAM-guided graphical LASSO, 35 and Fisher-von-Mises mixture modeling. 36 We find that all methods show high pairwise clustering coefficients (figure S1e), and differ predominantly by module splitting (figure 1e). For instance, most of the differences between ARACNe clusters and WGCNA clusters come from large ARACNe modules represented as...