Entrez

Entrez is a text-based search and retrieval system developed by the National Center for Biotechnology Information (NCBI) that provides unified access to a diverse set of biomedical databases. It is designed to allow researchers to search across multiple databases through a single interface and to navigate among related data via hyperlinks.

Entrez indexes data from NCBI databases such as PubMed, PubMed Central, Gene, Nucleotide, Protein, Genome, Structure, Taxonomy, SNP, GEO, and more. Users can perform fielded queries, use Boolean operators, apply filters and limits, and use the History server to combine results from different databases. Entrez provides linking between records, enabling navigation from, for example, a PubMed citation to related GenBank records, GEO datasets, or clinical variants.

Programmatic access is provided through the Entrez Programming Utilities (E-utilities), a set of REST-like services that support ESearch, EFetch, ESummary, ELink, and related functions, enabling automated search, retrieval and analysis. A complementary command-line package called EDirect is widely used to script Entrez workflows.

Entrez originated in the 1990s as part of the NCBI's effort to integrate its growing data collections; it remains a central component of NCBI's data infrastructure and an essential resource for literature and sequence data discovery, data mining, and bioinformatics workflows.