The Gene Expression Omnibus (GEO) is an international public repository that archives and freely distributes microarray, next-generation sequencing, and other forms of high-throughput functional genomic data sets (1). Approximately 90% of the data in GEO are gene expression studies that investigate a broad range of biological themes including disease, development, evolution, immunity, ecology, toxicology, metabolism, and more. The non-expression data in GEO represent other categories of functional genomic and epigenomic studies including those that examine genome methylation, chromatin structure, genome copy number variations, and genome–protein interactions. A breakdown of GEO data types and technologies is provided on the repository Summary page.