British Clematis Society
Promotes the cultivation and preservation of clematis; includes an advice section, listing of members' gardens, shows and events, and membership details.
Clematis on the Web
The University of Hull maintains a resource database for clematis growers and enthusiasts; includes a photo database of varieties, growing advice, and a listing of collections worth visiting.
Howells on Clematis
A collection of clematis articles, growing information, books, and links, maintained in memory of the late Dr John G Howells, 1918-2007.
National Collection of Clematis Montana
A guide to a collection of over two hundred Clematis Montana Group plants held in a Wiltshire garden; includes visitor guide, calendar, photos, and contacts.