The Basel Register of Thesauri, Ontologies & Classifications (BARTOC) is a database of Knowledge Organization Systems and KOS related Registries, developed by the Basel University Library, Switzerland. Its main goal is to list as many Knowledge Organization Systems as possible at one place in order to achieve greater visibility, highlight their features, make them searchable and comparable, and foster knowledge sharing. BARTOC includes any kind of KOS from any subject area, in any language, any publication format, and any form of accessibility. BARTOC’s search interface is available in 20 European languages and provides four search options: Basic Search by keywords, Advanced Search by taxonomy terms, GeoSearch by a map, and a known-item Title Finder search. A circle of editors has gathered around BARTOC from all across Europe and BARTOC has been approved by the International Society for Knowledge Organization (ISKO).