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. According to the Fundament of Esperanto, land names should generally be formed with the suffix -uj- meaning a container, so that for example Franco is a Frenchman, so France would be Francujo meaning that it is a container for Frenchmen, although this has largely been replaced by the pseudo-suffix -i- (hence Francio) in actual usage. For some countries -land- is recommended instead, e.g. Finnlando. (There is no obvious reason why the stem Finn- -- incidentally an exception to the "rule" that double consonants should not occur within a single stem -- should be followed by -land- rather than -uj- or -i-, though it may be reflecting similar inconsistencies in languages such as English or German.) The name of the "fictitious" Esperantoland is formed analogously to the official form Francujo, rather than to the usual (unofficial) form Francio or to Finnlando. Because the root does not indicate a people, but is the name of a language, this would mean literally a container for the language, and is hence an even further metaphorical abstraction from the normal meaning of -uj- as a physical container than is the case in Francujo etc. The term most analogous to Francujo would probably be Esperantistujo, but this is not used in practice. Perhaps Esperantio is more popular with younger Esperantists. For example, the Pasporta Servo uses the -io form.