This article is one of several in this issue about the Book of Commandments and Revelations, a foundational document of The Church of Jesus Christ of Latter-day Saints. This article orients readers to two important features of the Book of Commandments and Revelations: its index of contents and its historical headnotes. John Whitmer began to compile "The Index of the contents of this Book" in the back, on pages 207–8. It covers only the book's first 94 pages, ending in the summer of 1831. In some instances, it is obvious that he was not recording the revelations in their order of receipt. In other instances, particularly the earliest revelations, Whitmer's order of recording reflects a chronology of some events that differs from what has been assumed to be the historical order. Several pages of the BCR are missing, but in some instances the index of contents tells us what they recorded. From the very beginning of the Book of Commandments and Revelations, with few exceptions, John Whitmer penned a brief preface to each entry identifying the person or subject the commandment addressed. His terse prefaces are invaluable. They reveal heretofore unknown dates, places, chronologies, intentions, causes and effects, and meanings. Occasionally the headnotes challenge later sources.