The Liber Iesus or Book of the ABC (Trivulziano codex 2163) is a parchment codex containing a collection of prayers and short texts in Latin and vulgar prepared, as the so-called Grammatica del Donato, for Massimiliano Sforza, son of Ludovico il Moro, during the last five years of the fifteenth century. The elegant hand of the calligrapher Giovanni Battista Lorenzi can be recognized in the humanistic pose of the text. The decorative apparatus was entrusted to a main illustrator, identified with the anonymous Maestro dell'Epitalamio by Giasone del Maino. Only in two full-page miniatures (Meeting between Massimiliano Sforza and the Emperor of Austria and Massimiliano Sforza with Count Borella) is a second hand identified, Boccaccio Boccaccino according to some, Giovanni Antonio Boltraffio according to others. The choice to dedicate a prayer book to Massimiliano Sforza, alongside the so-called Grammatica del Donato, identifies the two areas (religious and civil) in which the good Renaissance prince called to rule a state had to be educated.

This work, belonging to the permanent collection, is open to the public for conservation reasons only on the occasion of temporary exhibitions.