This bilingual thesaurus organizes the key concepts of biodiversity sciences, in their basic and applied ecological components. It uses polyhierarchy and includes 818 reciprocal associative relationships. The 1654 French and English descriptors (designating 827 concepts) are enriched with a large number of synonyms (1860) and hidden variants (7020) in both languages. Concepts are grouped into 82 collections, by semantic categories, thematic fields and EBV classes (Essential Biodiversity Variables). Definitions are given with their sources. This resource is aligned with the international thesauri AGROVOC, GEMET (GEneral Multilingual Environmental Thesaurus) and EnvThes (Environmental Thesaurus), as well as with the ontology ENVO (Environment Ontology).