Network of European Museum Organizations
https://www.ne-mo.org/
List of Network members by country.

Museum Directory on Wikipedia
http://en.wikipedia.org/wiki/List_of_museums

Art Museums Worldwide
http://www.artcyclopedia.com/museums.html

European Network of Science Centres and Museums
http://www.ecsite.eu/members/directory
Searchable members directory.

The Association for Science and Discovery Centres (United Kingdom)
http://sciencecentres.org.uk/

Irish Science Centres Association Network (Ireland)
http://www.iscan.ie/

Austrian Science Center Network (Austria)
http://www.science-center-net.at/

Nordisk Science Center Forbund (Denmark)
http://www.nordicscience.net/

Libraries and Archives Directory
http://europa.eu/publications/libraries-archives/index_en.htm#40
A “directory” of EU institutions.

National Archives Directory
http://libguides.usc.edu/content.php?pid=22394&sid=1211712
A USC Libraries’ guide which links to the official web sites of national archives around the world.

List of Archives
http://en.wikipedia.org/wiki/List_of_archives
Wikipedia listing of national archives.

Historical Archives of the European Union
https://www.eui.eu/en/academic-units/historical-archives-of-the-european-union
Websites of the National or State Archives of the 25 Member States of the European Union.

Archives Portal Europe
https://www.archivesportaleurope.net/
Provides access to information on archival material from different European countries as well as information on archival institutions throughout the continent.

National Archives of the United Kingdom
http://www.nationalarchives.gov.uk/

ArchiveGrid
http://beta.worldcat.org/archivegrid/
A database for locating special collections worldwide. Search for family and corporate histories, personal papers, and historical records. Over 2,500 libraries, museums, and archives worldwide contribute collection descriptions.

Archive Finder
https://research.lib.buffalo.edu/archive-finder
A current directory describing over 206,200 collections of primary source material housed in thousands of repositories across the US, UK, and Ireland.

Oral History Online
http://historymatters.gmu.edu/mse/oral/online.html
Provides in-depth indexing to more than 2,700 collections of oral history in English from around the world, including many full-text transcripts, audio, and video.

WorldCat
https://research.lib.buffalo.edu/WorldCat
Enter a subject term and limit your search to "Archival Materials". Or use subject keywords such as sources or diaries or interviews or pamphlets or correspondence or personal narratives or archives.