The Aubin Tonalamatl is a pictorial codex that reads from top to bottom and from right to left. It originally included another two folios that have since been lost. The Tonalamatl (bark paper [or book] of the days) was used by Aztec priests in a divination ritual. Tonalli means “day” and amatl refers to paper made from the inner bark of trees of the genus Ficus. The work contains a religious calendar of 260 days, the Tonalpohualli, which was used as a ritual and daily devotional for the celebration of holidays and served as the basis of astrological birth-chart predictions. This liturgical calendar was part of a collection owned by Lorenzo Boturini Benaducci (1702−51) that was confiscated on his expulsion from New Spain in the mid-1740s. The codex appears to have passed through several hands before it was sold for 2,000 francs to Americanist Alexis Aubin on October 24, 1841, who purchased it from Frédéric de Waldeck; Waldeck had owned the manuscript since the early 1800s. Eugène Goupil, of Mexican and French origin, purchased Aubin’s large collection of Mesoamerican manuscripts, including this work, in 1889, and his widow donated it to the National Library of France in 1898. This precious manuscript was subsequently stolen and is currently in Mexico. Mexican authorities, who are refusing to return it, have entrusted it to the country’s National Institute of Anthropology and History (INAH).