The Introduction to The Letters of J. R. R. Tolkien is written by Humphrey Carpenter in order to explain how The Letters of J. R. R. Tolkien collection came about, and how he and Christopher Tolkien started working on it.
The introduction begins with Humphrey Carpenter recalling that towards the end of his life J.R.R. Tolkien was for a few weeks deprived of the use of his right arm. Telling his publisher that: "I found not being able to use a pen or pencil as defeating as the loss of her beak would be to a hen". The introduction then goes on to tell us that much of Tolkien's life was spent writing and that he was a very avid letter writer as well. In selecting the letters, Carpenter and Christopher Tolkien not only wanted to include letters which were obviously related to "Middle-earth" but also letters that showed Tolkien's mind, interests and view of the world.
Among the omissions is a very large body of letters who were of a personal nature, and only a few relevant passages of these are included in the book. (An omitted passage of a letter is shown by a row of four dots.) Tolkien's original writing has been left unaltered, except in the case of addresses and dates, which have been standardized. Some included letters are only based on drafts for those letters and might not reflect the final sent letter if a letter was sent at all. When a portion of a letter has been printed the opening address, the ending and signature have been omitted also footnotes to letters are Tolkien's own. Where necessary letters are preceded by a headnote in order to explain the context of the correspondence. All others are found at "Notes".
It is also assumed that a reader of this book would have a thorough knowledge of The Hobbit and The Lord of the Rings books. In the editorial notes four other books are cited by brief titles: Pictures, Unfinished Tales, J.R.R Tolkien - A Biography and The Inklings. The introduction then concludes with Carpenter explaining how exactly the Formation began and that he is grateful and thankful to all those lended him and Christopher letters, as well as to all the organisations and individuals who have helped him.