The basic principle underlying the organization of any library is to describe the documents it contains so that they may be located. All libraries create sets of records which describe the documents in their collections. Catalogs are sets of records to documents that share a location. Indexes are sets of records to documents that share some other attribute (generally subject matter). Corpora are collections of text. Catalogs, indexes, and corpora are created and/or maintained by various authorities (state or private, non-profit or commercial). Here you will find the most significant and representative catalogs, indexes, and corpora across major disciplines.