Some 1,200 publishers have set up stands in this huge exhibition space. The programme includes 500 talks and debates, and
most 4,500 book signings.
The guests of honour, among the thousands of invited authors, are 36 Mexican writers - including one of the country's greatest thinkers, Carlos Fuentes.
The theme of the fair is Mexico's diverse mosaic of literature.
The guests include writers who work in indigenous languages, like the Mayan poet Briceida Cuevas Cob.
And, with a special series of scientific lectures, the Book Fair is joining the celebrations for the International Year of Astronomy and the 200th anniversary of Charles Darwin's birth.