Esperanto is a constructed international auxiliary language. It is the most widely spoken constructed language in the world. An international auxiliary language (sometimes abbreviated as IAL or auxlang) or interlanguage is a language meant for communication between people from different nations who do not share a common first language. An auxiliary language is primarily a second language. This books provided a comprehensive and well-organized overview of the grammar with lots of examples and illustrations. It is easier to learn from than lessons, like most textbooks have. And in spite of the fact that the book is 100 years old, Esperanto hasn't changed enough to make any difference. Sure, people are more like to say "esperantio" than "esperantujo."