Esperantujo, also Esperantio, is a term used by speakers of the planned international language Esperanto to refer to the sphere of activity taking place in that language. When two people are speaking Esperanto, they are said to be "in" Esperantujo, although geographically they may be in Spain, Russia, or Canada. So understood, Esperantujo may have two "inhabitants," or many more, and it is everywhere.

The word is formed analogously to country names; in Esperanto some names of countries are formed from a base word that is the name of a people. This is done either with the original suffix UJ, or with the unofficial suffix I, or in some cases with the root LAND, eg. "Franco" ("Frenchman") => "Francujo", "Francio" (or "Franclando"). The name of the "fictitious" Esperantoland is analogously formed like this although the root does not indicate a people, but is the name of a language: "Esperantujo", "Esperantio" or "Esperantolando". For ordinary countries the I forms are more popular than the UJ forms, but in the case of Esperantoland, the UJ form is for some reason the most widely used one. Perhaps "Esperantio" is more popular with younger Esperantists. For example, the Pasporta Servo uses the -io form.