Zamenhof Day (Zamenhofa Tago in Esperanto), also called Esperanto Day, is celebrated on 15 December, the birthday of Esperanto creator L. L. Zamenhof. It is the most widely celebrated day in Esperanto culture.
The history of celebrating Esperanto on Zamenhof’s birthday can be traced back to 17 December 1878, when at a birthday party for his 19th birthday he presented to his friends his Lingwe universal, the first version of his international language. By 1887, this language had evolved into what is now recognized as Esperanto when he published the Unua Libro.
Today, many Esperanto speakers buy an extra Esperanto book around this time of year. There are also special Esperanto gatherings and parties throughout the world to celebrate the occasion, which is used as a reason for Esperantists to get together during the holiday season.
Some Esperanto speakers, not wanting to over-celebrate the achievements of a single man, have suggested celebrating 15 December as Esperanto Literature Day instead. Thus they encourage Esperanto organizations that hold gatherings on that day to add a book review or poetry reading to the program or to announce the publication of a new book. On an individual level, one can buy or start reading a new book or in some other way celebrate Esperanto literature.