ATOL (Animal Trait Ontology for Livestock) is an ontology of characteristics defining phenotypes of livestock in their environment (EOL). ATOL aims to: – provide a reference ontology of phenotypic traits of farm animals for the international scientificand educational – communities, farmers, etc.; – deliver this reference ontology in a language which can be used by computers in order to support database management, semantic analysis and modeling; – represent traits as generic as possible for livestock vertebrates; – make the ATOL ontology as operational as possible and closely related to measurement techniques; – structure the ontology in relation to animal production.