The Open Biological and Biomedical Ontologies (OBO) Foundry is a group of people dedicated to build and maintain ontologies related to the life sciences. The OBO Foundry establishes a set of principles for ontology development for creating a suite of interoperable reference ontologies in the biomedical domain. Currently, there are more than a hundred ontologies that follow the OBO Foundry principles. The OBO Foundry effort makes it easier to integrate biomedical results and carry out analysis in bioinformatics. It does so by offering a structured reference for terms of different research fields and their interconnections (ex: a phenotype in a mouse model and its related phenotype in zebrafish). Introduction The Foundry initiative aims at improving the integration of data in the life sciences. One approach to integration is the annotation of data from different sources using controlled vocabularies. Ideally, such controlled vocabularies take the form of ontologies, which support logical reasoning over the data annotated using the terms in the vocabulary. The formalization of concepts in the biomedical domain is especially known via the work of the Gene Ontology Consortium, a part of the OBO Foundry. This has led to the development of certain proposed principles of good practice in ontology development, which are now being put into practice within the framework of the Open Biomedical Ontologies consortium through its OBO Foundry initiative. OBO ontologies form part of the resources of the National Center for Biomedical Ontology, where they form a central component of the NCBO's BioPortal. Open Biological and Biomedical Ontologies The Open Biological and Biomedical Ontologies (OBO; formerly Open Biomedical Ontologies) is an effort to create ontologies (controlled vocabularies) for use across biological and medical domains. A subset of the original OBO ontologies has started the OBO Foundry, which leads the OBO efforts since 2007. The creation of OBO in 2001 was largely inspired by the efforts of the Gene Ontology project. OBO forms part of the resources of the U.S. National Center for Biomedical Ontology (NCBIO) and a central element of the NCBO's BioPortal. It is an initiative led by the OBO Foundry. Rules for participation The OBO Foundry is open to participations of any interested individuals. Ontologies that intend to be officially part of the OBO Foundry have to adhere to the OBO principles and pass a series of reviews done by the members, when "the Foundry coordinators serve as analogs of journal editors". There are