It is one of the most important documents for researching the history of board games. The only known original is held in the library of the monastery of San Lorenzo del Escorial near Madrid in Spain. The book is bound in sheepskin and is 40 cm high and 28 cm wide (16 in × 11 in). A 1334 copy is held in the library of the Historical Academy of Madrid.
The Libro de juegos contains an extensive collection of writings on chess, with over 100 chess problems and variants. Among its more notable entries is a depiction of what Alfonso calls the ajedrex de los quatro tiempos ("chess of the four seasons"). This game is a chess variant for four players, described as representing a conflict between the four elements and the four humors. The chessmen are marked correspondingly in green, red, black, and white, and pieces are moved according to the roll of dice. Alfonso also describes a game entitled "astronomical chess", played on a board of seven concentric circles, divided radially into twelve areas, each associated with a constellation of the Zodiac.
The book describes the rules for a number of games in the tables family. One notable entry is todas tablas, which has an identical starting position to modern backgammon and follows the same rules for movement and bearoff. Alfonso also describes a variant played on a board with seven points in each table. Players rolled seven-sided dice to determine the movement of pieces, an example of Alfonso's preference for the number seven.