Expression quantitative trait loci (eQTL) are genetic variations that affect gene expression. Several eQTL databases have been created to allow researchers to look up genetic loci that are associated with gene expression and in different types of tissues and cells. In the pgrn.org Tools webapp, we curated several key eQTL databases, such as eQTL of the blood, intestine, immune cells, kidney, lung and monocytes. The most popular eQTL database is GTEx Portal, which has measured transcription levels of genes in 53 tissues using RNAseq and also eQTL for 44 different tissues in over 7000 samples (ref). The GTEx database allows users to view and download computed eQTL results (link). The datasets serve as useful resource for additional kinds of analyses and it is widely used by researchers to inform the genetic association of their genomewide association studies (ref, ref, ref) or to validate findings from in vitro assays. Below are a few examples that are valuable resources. Should you know of any eQTL databases, which are missing from the Tools webapp, please contact email@example.com. Please visit pgrn.org/tools to check out other tools.