The Book of the Chapter is Albert G. Mackey’s seminal work on the degrees of Royal Arch Masonry as practiced in the American York Rite system. First published in 1858, the book offers both a practical guide and a symbolic interpretation of the Capitular degrees: Mark Master, Past Master, Most Excellent Master, and the Royal Arch. Mackey, one of the most influential Masonic scholars of the 19th century, presents the rituals and ceremonies with precision, while also providing historical commentary and philosophical reflections. His analysis reveals the deeper esoteric structure of the Chapter system, positioning it as the spiritual completion of Craft Masonry and the restoration of the Lost Word. Far from being a mere manual, this work is a gateway to the inner meaning of the Capitular tradition. It remains an essential resource for Royal Arch Masons and students of Masonic symbolism alike.