Esperanto
- Universala Esperanto-Asocio [central organization for Esperanto in the world]
- Akademio de Esperanto [highest authority on Esperanto]
- Esperanto-Ligo en Israelo [central organization for Esperanto in Israel]
- Japana Esperanto-Instituto [central organization for Esperanto in Japan]
- Kansaja Ligo de Esperanto Grupoj [central organization for Esperanto in Kansai area, Japan]
- Virtuala Esperanto-Biblioteko [Internet resources on Esperanto]
- Esperanto Panorama [Internet resources on Esperanto]
- Esperanto Access [info about Esperanto in English]
- Esperantic Studies Foundation [linguistic studies of Esperanto and interlingual communication]
- Esperantologio [linguistic studies of Esperanto]
- Lernu! [online course of Esperanto in various languages]
- Plena Manlibro de Esperanta Gramatiko [grammar of Esperanto]
- Monato [online version of a monthly newsmagazine in Esperanto]
Esperanto: Electronic Sources
- eLibrejo [collection of freely downloadable electronic books in Esperanto]
International Planned Languages
- Society for Interlinguistics [international organization for the study of planned languages]
- Constructed Human Languages [Internet resources on planned languages]
- Constructed Languages [Internet resources on planned languages]
- Uniono por la Linguo Internaciona Ido [central organization for Ido]
- Interlingue-Union [central organization for Interlingue (Occidental)]
- Union Mundial pro Interlingua [central organization for Interlingua]
- BJA-LISTO [mailing list on social interlinguistics]