All the World's Rotorcraft
- Provides pictures and background from the first designs to current machines. Also offers dictionary and links to related resources.
- http://avia.russian.ee/

Helicopters and Autogiros 1939 to 1945
- Aviation history in the WWW: Index of aircraft by category and time period.
- http://www.luftfahrtmuseum.com/htmi/itk/h4.htm

Igor I. Sikorsky Historical Archives, Inc.
- Dedicated to acquiring, preserving and protecting the historical materials that chronicle the aviation careers of Igor Sikorsky, the companies he founded and the accomplishments of its employees.
- http://www.sikorskyarchives.com//

Helicopter History Site
- This site traces the evolution of rotary wing aircraft back to Leonardo Da Vinci.
- http://www.helis.com