'The International Auxiliary Language Esperanto' is a book written by George Cox, where he explains the history, purpose, and advantages of Esperanto, a language designed to be a common second language for the world. By learning Esperanto, people of all nationalities can easily correspond on any topic, read books in translation, and participate in international congresses without the need for interpreters. The book includes a comprehensive grammar and commentary section, exercises, and useful lists of primary words and phrases. Cox's work highlights the potential of Esperanto to facilitate communication and understanding across borders, making it an essential read for anyone interested in language, culture, and international relations.