The longest book in the Book of Mormon is the book of ALMA, which is four letters long. The book of ALMA is the longest book in the Book of Mormon and is named after a prophet-warrior who was a contemporary of Nephi, the first Book of Mormon prophet. It contains an account of the wars and contentions among the Nephites and Lamanites. It also contains teachings of ALMA and his sons, as well as the conversion of many people to the gospel of Jesus Christ.