Representing experimental variables with EFO

The Experimental Factor Ontology (EFO) provides a systematic description of many experimental variables available in EBI databases, and for projects such as the GWAS catalog. It combines parts of several biological ontologies, such as UBERON anatomy, ChEBI chemical compounds, and Cell Ontology. The scope of EFO is to support the annotation, analysis and visualization of data handled by many groups at the EBI and as the core ontology for Open Targets. EFO is developed by the EMBL-EBI Samples, Phenotypes and Ontologies Team (SPOT). We also add terms for external users when requested. If you are new to ontologies, there is a blog post by James Malone on what ontologies are for.


Browse EFO with EBI's OLS or The NCBO BioPortal (external). You can also search EFO using the search box, above. The EFO source ontology can be viewed on GitHub at


Submit new terms or report bugs using our GitHub issue tracker or if you prefer to e-mail us please contact efo-users [at] For EFO announcements and monthly updates please join the efo-users public mailing list efo-users public mailing list.


Download the latest release of EFO in OWL format (inferred) or the OBO format version. Read the latest Release Notes. You can also get previous releases by release version e.g.


Read more about EFO or see the Frequently Asked Questions. You can also read about ontologies in James Malone's blog. To cite EFO see the publication here.


We provide tools to support the development and use of EFO such as OxO, Zooma, and OntoString.


Please email the EFO user list with any questions or comments. EFO is released under the Apache 2.0 license and with the following terms of use.