"The Scapular Devotion: Origin, Legislation, and Indulgences Attached to the Scapular" by P.E. Magennis (1923) is a comprehensive guide to the Brown Scapular devotion. This book examines the history, theological basis, canonical rules, and indulgences granted by the Catholic Church to those who wear it, particularly those within the Carmelite order.

It explains the history of the Scapular devotion, particularly its connection to the tradition of the apparitions of the Virgin Mary to St. Simon Stock, which has its roots in the Carmelite order. It then updates and explains the rites of blessing, wearing, and obligations associated with the Scapular according to Church law at the time. It also details the various indulgences (forgiveness of sins) attached to the wearing of the Brown Scapular, approved by Vatican authorities.

This book is an essential classic resource for Catholics seeking to understand the theological foundations and discipline of the Brown Scapular devotion. Digital versions of this work can often be found on Catholic historical archives.