The Cell Ontology is designed as a structured controlled vocabulary for cell types. This ontology was constructed for use by the model organism and other bioinformatics databases, where there is a need for a controlled vocabulary of cell types. This ontology is not organism specific; indeed it includes cell types from prokaryotes to mammals, including plants and fungi. A full description of the Cell Ontology can be found in Bard, Rhee and Ashburner. 2005. An Ontology for Cell Types.