[3] On this day, Esperantists hold information sessions and cultural gatherings to promote literature in Esperanto.

[4][5] By 1887, this language had evolved into what is now recognized as Esperanto when he published the Unua Libro.

[8][9] 15 December 2009 marked 150 years since Zamenhof's birth, and there were several events to celebrate.

On this date, the authorities in his home town of Białystok, Poland, opened a new Zamenhof Center,[10] and a symposium honoring Zamenhof was held in New York City, featuring talks by Arika Okrent and Humphrey Tonkin among other professors.

[11] Also on this date, the search engine Google, in 33 national language versions (but not the international English one), bore a special version of their logo (a Doodle) emblazoned with the Esperanto flag in honor of the occasion,[12][13] which generated, between the 30 biggest Wikipedia languages, 1,750,000 page views on the articles "L. L.