120px, The Entrez logo The Entrez (pronounced ''ɒnˈtreɪ'') Global Query Cross-Database Search System is a federated search engine, or web portal that allows users to search many discrete
health sciences The following Outline (list), outline is provided as an overview of and topical guide to health sciences: Health sciences – are those sciences which focus on health, or health care, as core parts of their subject matter. These two subject ...
databases at the
National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The N ...
(NCBI) website. The NCBI is a part of the
National Library of Medicine The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library. Located in Bethesda, Maryland Bethesda is an unincorporated area, unincorporated, census-designate ...
(NLM), which is itself a department of the
National Institutes of Health The National Institutes of Health (NIH) () is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late 1880s and is now part of the United States Department of Health an ...
(NIH), which in turn is a part of the
United States Department of Health and Human Services The United States Department of Health and Human Services (HHS), also known as the Health Department, is a Cabinet of the United States, cabinet-level United States federal executive departments, executive branch department of the U.S. federal g ...
. The name "Entrez" (a greeting meaning "Come in" in French) was chosen to reflect the spirit of welcoming the public to search the content available from the NLM. Entrez Global Query is an integrated search and retrieval system that provides access to all databases simultaneously with a single query string and user interface. Entrez can efficiently retrieve related sequences, structures, and references. The Entrez system can provide views of
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing m ...
sequences and
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaperone proteins, bind to and condense the DNA molecule ...

maps. Some textbooks are also available online through the Entrez system.


The Entrez front page provides, by default, access to the global query. All databases indexed by Entrez can be searched via a single query string, supporting
boolean operators Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean. Related to this, "Boolean" may refer to: * Boolean data type, a form of data with only two possible values (usually "true" and "false") ...
and search term tags to limit parts of the search statement to particular fields. This returns a unified results page, that shows the number of hits for the search in each of the databases, which are also links to actual search results for that particular database. Entrez also provides a similar interface for searching each particular database and for refining search results. The Limits feature allows the user to narrow a search a web forms interface. The History feature gives a numbered list of recently performed queries. Results of previous queries can be referred to by number and combined via boolean operators. Search results can be saved temporarily in a Clipboard. Users with a MyNCBI account can save queries indefinitely and also choose to have updates with new search results e-mailed for saved queries of most databases. It is widely used in the field of biotechnology as a reference tool for students and professionals alike.


Entrez searches the following databases: *
PubMed PubMed is a free search engine accessing primarily the MEDLINE MEDLINE (Medical Literature Analysis and Retrieval System Online, or MEDLARS Online) is a bibliographic database of life sciences and biomedical information. It includes bibliograp ...
: biomedical literature citations and abstracts, including
Medline MEDLINE (Medical Literature Analysis and Retrieval System Online, or MEDLARS Online) is a bibliographic database of life sciences and biomedical information. It includes bibliographic information for articles from academic journal An academic or ...
- articles from (mainly
medical Medicine is the art, science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explana ...
) scientific journal, journals, often including abstracts. Links to PubMed Central and other full-text resources are provided for articles from the 1990s. *PubMed Central: free, full-text journal articles *Site Search: NCBI web and FTP web sites *Books: online books *Online Mendelian Inheritance in Man (OMIM) *''Nucleotide'': sequence database (GenBank) *''Protein'': sequence database *''Genome'': whole genome sequences and Human Genome Project, mapping *''Structure'': three-dimensional macromolecular structures *''Taxonomy'': organisms in GenBank Taxonomy *''dbSNP'': single nucleotide polymorphism *''Gene (database), Gene'': gene-centered information *''HomoloGene'': eukaryotic homology groups *PubChem Compound: unique small molecule chemical structures *PubChem Substance: deposited chemical substance records *Genome Project: genome project information *UniGene: gene-oriented clusters of transcript sequences *''Conserved domain database, CDD'': conserved protein domain database *''PopSet'': population study data sets (epidemiology) *''GEO Profiles'': expression and molecular abundance profiles *''GEO DataSets'': experimental sets of GEO data *''Sequence read archive'': high-throughput sequencing data *''Cancer Chromosomes'': cytogenetic databases *''PubChem BioAssay'': bioactivity screens of chemical substances *''Probe'': sequence-specific reagents *''NLM Catalog'': NLM bibliographic data for over 1.2 million journals, books, audiovisuals, computer software, electronic resources, and other materials resident in LocatorPlus (updated every weekday).


In addition to using the search engine forms to query the data in Entrez, National Center for Biotechnology Information, NCBI provides the Entrez Programming Utilities (eUtils) for more direct access to query results. The eUtils are accessed by posting specially formed URLs to the NCBI server, and parsing the XML response. There was also an eUtils SOAP (protocol), SOAP interface which was terminated on July 2015.


In 1991, Entrez was introduced in CD form. In 1993, a client-server version of the software provided connectivity with the internet. In 1994, NCBI established a website, and Entrez was a part of this initial release. In 2001, Entrez bookshelf was released and in 2003, the Entrez Gene database was developed.



External links

Entrez search engine form

Entrez Help
Online databases National Institutes of Health Biological databases Government-owned websites of the United States Scholarly search services