"So the sympathy of a friend gives plainness and point to my speech.
----Journal, 29 December 1840
Many scholars and editors, most notably the late Walter Harding, have contributed to the three-volume set of correspondence in the Princeton Edition of The Writings of Henry D. Thoreau. Correspondence 1: 1834-1848, edited by Professor Robert Hudspeth, was published by Princeton University Press on August 1, 2013. Correspondence 2: 1849-1856 is in production, and work on Correspondence 3: 1857-1862 is ongoing.
As of July 2015, six libraries have scanned and digitized some or all of their manuscripts of letters: the Abernethy Library at Middlebury College, the Beinecke Library at Yale University, the Berg Collection at the New York Public Library, the Harry Ransom Center at the University Of Texas at Austin, the Houghton Library at Harvard University, and the John Hay Library at Brown University. Links to letters to and from Thoreau that are included in these digital collections can be found at Correspondence 1-3.
A LIST OF THOREAU'S LETTERS
Divided chronologically into three sections, this is a complete list
of all extant letters, whether in manuscript or print form. The list notes
whether the letter is to (t) or from (f) Thoreau, notes editorial additions
in brackets, includes the name of correspondents and their location, and
provides manuscript and repository information. A key to abbreviations
used follows each list.