Spain is a biodiversity hotspot that hosts small rear-edge populations of species typical of central and northern Europe, Mediterranean and Macaronesian biota, many marine species, and a large set of endemic organisms. Spain Species Specialist Group (EsSSG) is a science-based network of volunteer experts belonging to universities, scientific and conservation associations, the SSC Centre for Species Survival Macaronesia, the Spanish Ministry for Ecological Transition and Demographic Challenge (MITECO), and the Spanish National Committee of IUCN (CeUICN), all of them working together toward conserving nature through providing scientific knowledge,conservation expertise, and positive action to both prevent the loss and aid recovery of the diversity of life on the land, freshwaters, and marine waters under the jurisdiction of the Spanish State. The CeUICN is its host institution.