Characterizing the collective regulatory impact of genetic variants on complex phenotypes is a major challenge in developing a genotype to phenotype map. Using expression quantitative trait locus (eQTL) analyses, we constructed bipartite networks in which edges represent significant associations between genetic variants and gene expression levels and found that the network structure informs regulatory function. We show, in 13 tissues, that these eQTL networks are organized into dense, highly modular communities grouping genes often involved in coherent biological processes. We find communities representing shared processes across tissues, as well as communities associated with tissue-specific processes that coalesce around variants in tissue-specific active chromatin regions. Node centrality is also highly informative, with the global and community hubs differing in regulatory potential and likelihood of being disease associated.GTEx | expression quantitative trait locus | eQTL | bipartite networks | GWAS M ore than a decade after the sequencing of the human genome, our understanding of the relationship between genetic variation and complex traits remains limited. Genomewide association studies (GWASs), which look for association between common genetic variants and phenotypic traits, have resoundingly shown that complex phenotypes are influenced by many variants of relatively small effect size (1, 2), the overwhelming majority of which (∼93%) lie in noncoding regions of the genome (3, 4). Those single-nucleotide polymorphisms (SNPs) associated with complex traits are enriched for variants likely to affect gene expression, as measured by expression quantitative trait locus (eQTL) analysis (5), suggesting that they influence phenotypes through changes in gene regulation (6, 7). Identifying the regulatory role of these variants likely also depends on the tissues relevant to the phenotype. For example, eQTL identified in skeletal muscle and adipose tissues for type 2 diabetes (T2D) have been shown to explain a greater proportion of the disease heritability than those identified across tissues (8). Furthermore, variants far from the transcriptional start site (TSS) of a gene, trans-eQTL, explain more of the heritability of T2D than those near the gene, cis-eQTL, and there is mounting evidence for the importance of these variants in a variety of phenotypes (9-11). That trans-eQTL, which can influence hundreds of genes in humans (12), might have an impact on the phenotype is consistent with similar observations in model organisms (13). However, large-scale detection of trans-eQTL across populations and tissues (14) has only recently become feasible in humans, and our understanding of how multiple cis-and trans-eQTL influence gene expression and cellular functions in different tissues is incomplete.We performed a systems genetics analysis of the regulatory effects of common [minor allele frequency (MAF) >5%] variants in 13 tissues collected by the Genotype-Tissue Expression (GTEx) consortium. By constructing tissue-leve...