The central act of Christian worship is the Mass or Eucharist. This, however, is a formal public act, and generally a once-in-a-week event, which does not entirely answer the spiritual aspirations of the vast majority of Christians who express these through prayer and "devotional practices". The cult of relics and of saints in general; banding together into confraternities to foster a special devotion; going on pilgrimages, wearing medals, badges and scapulars - all these are forms of devotion. Where did they all come from? They have left their mark on the Church, in the history of books and in manuals of prayers, but relatively little is known about them. The idea for this book arose when, in the senior common room of a university theological faculty, it became clear that none of those present knew why there was an "Infant of Prague". The book is in a dictionary format. Mainly historical in its approach, it explains how a particular devotion arose, sets it in its context and explains the purpose it served in the life of the Church. It is critical without being judgemental on subjects such as the "truth" behind apparitions of the Virgin Mary. Some 600 entries range over topics such as relics, pilgrimages and the cult of the saints, as well as more specialized and local devotions. The work is designed to be of use to historians and those engaged in religious studies, as well as being of interest to the general public. The topics are confined to the Christian religion and, in effect, almost entirely to the Roman Catholic tradition. Tables provide a comparison of the Liturgical Calendar (fixed and moveable feasts) before and after the Reform of 1969. A comprehensive index enables readers to follow virtually any subject through its different aspects, as well as providing a quick guide to the contents of the dictionary. Michael Walsh is the editor of Bishop Butler's "Lives of the Saints" in one concise volume, and the author of a companion volume, "Patron Saints".