In Mormonism, the Letter of Appointment is a controversial two-page document used by the supporters of James Strang to prove that he was the designated successor to Joseph Smith, Jr. as prophet and head of the Latter Day Saint movement.

The letter from Smith to Strang is now preserved at Yale University. Experts agree that the postmark (from Nauvoo, Illinois a week prior to Smith's assassination on June 27, 1844) and the first page are genuine, but most have denounced the purported second page of the letter (the one in which Smith's appointment of Strang as his successor is made) as a forgery, largely upon the basis of the paper being of differnt stock than that of the first.

Strang also claimed to have received an angelic appointment at a time coincident with Smith's death, and like Smith claimed the ability to translate ancient documents on metal plates into modern English, which was sufficient for him to attract a significant group of followers within the LDS movement until his own assassination 12 years later; but his following paled in comparison with the one attracted by Brigham Young which came to constitute the Church of Jesus Christ of Latter-day Saints, the "mainstream" Mormon movement. Some Strangites, in contrast, after Strang's death turned to Joseph Smith III for leadership and became the nucleus of the Reorganized Church of Jesus Christ of Latter Day Saints, now referred to as the Community of Christ, the second-largest Mormon denomination, while others remained within the group founded by Strang.