Sources: InU-Li
- Samuel L. Clemens to Charles Henry Webb, 25 November 1867 · Washington, D.C · UCCL00160 InU-Li
- SLC to Unidentified, 31 October 1869 · Pittsburgh, Pa · UCCL10818 InU-Li
- Samuel L. Clemens to Charles Warren Stoddard, 27 or 28 October 1877 · (1st of 5) · Hartford, Conn · UCCL09289 InU-Li
- Samuel L. Clemens to Unidentified, December 1880 · Hartford, Conn · UCCL10817 InU-Li
- SLC to Stewart L. Woodford, 14 December 1882 · Hartford, Conn · UCCL10835 InU-Li
- SLC to Oscar Marshall, 21 March 1885 · New York, N.Y · UCCL09337 InU-Li
- SLC to William D. Foulke and E. W. Halford, 3 October 1888 · Hartford, Conn · UCCL03780 InU-Li
- SLC to Robert U. Johnson, 16 August 1889 · Elmira, N.Y · UCCL10828 InU-Li
- SLC to Richard Watson Gilder, 17 August 1889 · Elmira, N.Y · UCCL10829 InU-Li
- SLC to James W. Riley, 29 December 1890 · Hartford, Conn · UCCL10831 InU-Li
- SLC to James W. Riley, 2 February 1891 · Hartford, Conn · UCCL04165 InU-Li
- Edgar W. (Bill) Nye to SLC, 22 February 1893 · San Francisco, Calif. · UCLC45915 InU-Li
- SLC to Chatto & Windus, 5 August 1893 · Krankenheil, Germany · UCCL04431 InU-Li
- SLC to James W. Riley, 16 January 1898 · Vienna, Austria · UCCL10832 InU-Li
- SLC to J. Henry Harper, 30 August 1898 · Kaltenleutgeben, Austria · UCCL05429 InU-Li
- Samuel S. McClure to SLC, 6 February 1900 · UCLC48342 InU-Li
- SLC to Richard Watson Gilder, 6 July 1900 · Willesden, England · UCCL10830 InU-Li
- SLC to Edmund C. Stedman, 7 November 1900 · New York, N.Y · UCCL10834 InU-Li
- SLC per Isabel V. Lyon to John M. Dickey, 19 November 1902 · Riverdale, N.Y · UCCL10827 InU-Li
- SLC to James W. Riley, 27 July 1903 · Elmira, N.Y · UCCL10833 InU-Li
- SLC to Thomas S. Barbour, 22 September 1905 · Dublin, N.H · UCCL10820 InU-Li
- SLC per IVL to John Larkin, 13 January 1906 · New York, N.Y · UCCL10823 InU-Li
- SLC to Isabel V. Lyon, 14 March 1906 · New York, N.Y · UCCL10822 InU-Li
- SLC to Melville E. Stone, September 1906 · Unknown place · UCCL10878 InU-Li
- SLC to George B. Harvey, 11 or 12 September 1906 · Dublin, N.H · UCCL07520 InU-Li
- SLC to Isabel V. Lyon, 20 September 1906 · New York, N.Y · UCCL07527 InU-Li, CU-MARK
- SLC to George Parsons, 29 July 1907 · Tuxedo Park, N.Y · UCCL07794 InU-Li
- SLC to Isabel V. Lyon, 30 September 1907 · Tuxedo Park, N.Y · UCCL10819 InU-Li
- SLC to Melville E. Stone, 19 September 1908 · Redding, Conn · UCCL08097 InU-Li
- SLC to Ralph W. Ashcroft, 10 October 1908 · Redding, Conn · UCCL10824 InU-Li
- SLC to Pilgrims President, 5 November 1908 · Redding, Conn · UCCL08156 InU-Li
- SLC to Jean Clemens, 2 January 1909 · Redding, Conn · UCCL08306 InU-Li
- SLC to Norman Hapgood, Unknown date, New York, N.Y · UCCL10825 InU-Li
1