According to the Book of Mormon, the plates of Nephi, consisting of the large plates of Nephi and the small plates of Nephi, are a portion of the collection of inscribed metal plates which make up the record of the Nephites. This record was later abridged by Mormon and inscribed onto gold plates from which Joseph Smith translated the Book of Mormon after an angel revealed to him the location where the plates were buried on a hill called Cumorah near the town of Palmyra, New York.
Palaeographic study of the plates is not possible; according to Joseph Smith the plates were returned to an angel named Moroni, and are no longer in human possession.
According to the Book of Mormon prophet Nephi: "I make an abridgment of the record of my father, upon plates which I have made with mine own hands; wherefore, after I have abridged the record of my father then will I make an account of mine own life." Nephi's father, Lehi, was also a prophet who, after prophesying of the destruction of Jerusalem, left with members of his extended family around 600 BC and was eventually directed to the New World. Nephi was commanded to make two sets of plates: A small set of plates "for the special purpose that there should be an account engraven of the ministry of my people," and "the other plates are for the more part of the reign of the kings and the wars and contentions of my people." These plates, as well as other records made and found by Nephi's people were handed down from generation to generation.
After Nephi had begun the large plates, he was instructed by the Lord to make another set of plates to record "the ministry and the prophecies, the more plain and precious parts of them." These smaller plates were kept by Nephi's descendants until about 150 BC, when the prophet Amaleki delivered the plates to Benjamin, king of Zarahemla, who "put them with the other plates, which contained records which had been handed down by the kings" . Amaleki's last writing was the statement that the small plates were full and from this point there were no further additions to the small plates. Mormon did not abridge the small plates of Nephi but he did include them in the records he gave to his son Moroni .
The first six books of the Book of Mormon, from First Nephi to Omni are said to be a translation of the small plates of Nephi.
Joseph Smith said the large plates of Nephi were continually maintained until about AD 385, when the prophet Mormon, seeing that the destruction of the Nephite nation was imminent, abridged the large plates of Nephi. This abridgement, with additions by Mormon's son, Moroni, was part of the set of gold plates Moroni delivered to Joseph Smith.
The books within the Book of Mormon from The Words of Mormon to Fourth Nephi, are taken from Mormon's abridgment of the large plates. Although the large plates were intended for the more secular history of the Nephites, it is obvious from the version available in the Book of Mormon that there was a good deal of spiritual content as well, including sermons, prophecies and moral lessons. Some periods of time are covered in more detail than others, in particular a series of wars between the Nephites and the Lamanites in the Book of Alma. Whether the uneven coverage is a reflection of the original record or is an artifact of Mormon's abridgement is not clear from the text.
While recording his own history, Nephi mentioned "the record which has been kept by my father" in a few places. Nephi also mentioned that he had made an abridgement of the record of his father at the beginning of his own record.
While translating the gold plates, Joseph Smith reluctantly allowed his associate, Martin Harris, to take the entirety of the translation to that point, 116 manuscript pages, to show to Harris's wife and her family, to convince them that his (Harris's) financial support of Smith was worthwhile. Although strictly charged to ensure its safety, Harris lost the manuscript. The lost portion, part of the large plates of Nephi, contained Nephi's record of his father, Lehi's, ministry and was known as The Book of Lehi. Joseph Smith recorded, in the Doctrine and Covenants, sections 3 and 10, that the Lord instructed him not to re-translate the portion of the book that was lost but to continue forward.
In place of the lost Book of Lehi, the translation from the small plates of Nephi was used, which covered the same time period. Both Nephi and Mormon recorded that the small plates were made for a "wise purpose" that was known to the Lord. The aforementioned sections of the Doctrine and Covenants (D&C 3, D&C 10) state that the loss of the Book of Lehi was foreseen by the Lord and that it was for this purpose that the small plates were provided.
The Plates of Laban, Sword of Laban, the Plates of Nephi, Liahona, Plates of Ether, other records engraven on metal plates, and at least one record engraven upon stone were passed down from generation to generation. Each generation had one caretaker who was responsible for these items, mostly records; caretaker for more than their own record(s). Here is the list of caretakers, according to the Book of Mormon: