When I published _Dear Mark Twain: Letters from His Readers_ in 2013, I promised eventually to donate all my research files to the Mark Twain Papers and Project in Berkeley. As I explained in a note at the back of the book, the citations in the book's annotations represented only a small fraction of the sources on which the annotations drew. Well, I have now delivered all the book's research files to the Project. They cover not only the 200 letters published in _Dear Mark Twain_ but also more than 300 other letters not in the book. These materials include copies of my research correspondence; census reports; passport applications; ship passenger lists; newspaper and magazine articles; extracts from books, school yearbooks, and industrial publications; etc. As you may expect, most of the material pertains to Mark Twain's correspondents, under whose names it is organized in more than 500 files, which contain perhaps 10,000 pages. Scholars interested in consulting the files should contact the Project, which may need some integrating them into its collections.