ISIL Homepage
http://biblstandard.dk/isil/index.htm

An ISIL country code is the equivalent of the codes specified in ISO 3166-1.
See ISO 3166-1 decoding table:
http://www.iso.ch/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/iso_3166-1_decoding_table.html

ISIL is developed within the framework of Technical Committee 46/Subcommittee 4 (TC46/SC4)
TC 46 - Information and Documentation - SC 4 - Technical Interoperability
SC4 at ISO homepage

International Organization for Standardization
http://www.iso.ch/iso/en/ISOOnline.frontpage

If you want to buy the standard, please contact national member body of ISO:
http://www.iso.ch/iso/en/aboutiso/isomembers/MemberCountryList.MemberCountryList
or go to ISO 15511 in ISO Catalogue

Danish Agency for Libraries and Media (English text):
http://www.bibliotekogmedier.dk/english/

Styrelsen for Bibliotek og Medier (Danish text):
http://www.bibliotekogmedier.dk