Sources: NNPM
- Samuel L. Clemens to Shirley Brooks, 23 September 1873 · London, England · UCCL00963
- Samuel L. Clemens to the Editor of the Hartford Courant, 13 April 1874 · Hartford, Conn · UCCL01077
- SLC to James R. Osgood, 5 January 1883 · Hartford, Conn · UCCL02320
- SLC to Charles A. Dana, 11 July 1883, Elmira, N.Y · UCCL13323
- SLC to Elsie Leslie, 5 October 1889 · Hartford, Conn · UCCL03946
- OLC to Elsie Leslie, 15 May 1890 · Hartford, Conn · UCCL10702
- SLC to Martha B. Baldwin, 27 September–13 June 1893 · Florence, Italy · UCCL08603
- Jean Clemens to William Wilberforce Baldwin, 27 September–13 June 1893 · Florence, Italy · UCCL08602
- SLC to William Wilberforce Baldwin, 11 December 1892 · Florence, Italy · UCCL04305
- SLC to William Wilberforce Baldwin, 28 December 1892 · Florence, Italy · UCCL04315
- SLC to William Wilberforce Baldwin, 4 June 1893 · Florence, Italy · UCCL04411
- SLC to Elsie Leslie, 25 December 1893 · New York, N.Y · UCCL04538
- SLC to Richard Watson Gilder, 29 April 1898 · Vienna, Austria · UCCL05381
- SLC to William Knight, 24 June 1899 · London, England · UCCL05642
- SLC to Helen F. Levy, 27 July 1900 · London, England · UCCL08685
- SLC to William D. Howells, 13 November 1902 · Riverdale, N.Y · UCCL10884
- SLC to J. Pierpont Morgan, 28 November 1902 · New York, N.Y · UCCL13355
- Clara L. Clemens to William Wilberforce Baldwin, May 1904 · Florence, Italy · UCCL08600
- SLC to William Wilberforce Baldwin, 19 May 1904 · Florence, Italy · UCCL06837
- Clara L. Clemens to William Wilberforce Baldwin, 19 May 1904 · Florence, Italy · UCCL08601
- SLC to William Wilberforce Baldwin, 6 June 1904 · Florence, Italy · UCCL06857
- SLC to William Wilberforce Baldwin, 22 June 1904 · Florence, Italy · UCCL06882
- SLC to IVL, September 1905 · Dublin, N.H · UCCL13531
- SLC to IVL, September 1905 · Dublin, N.H · UCCL13530
- SLC to Clara L. Clemens, 1 October 1905 · Dublin, N.H · UCCL07156
- SLC to Anne E. Benjamin, 29 August 1906 · Dublin, N.H · UCCL07511
- SLC to Helen Keller, 14 November 1908 · Redding, Conn · UCCL08159
- SLC to John P. Morgan, 15 September 1909 · Redding, Conn · UCCL08452
- SLC to Clara L. Clemens, 21 February–23 February 1910 · Hamilton, Bermuda · UCCL08561
- SLC to Unidentified, 24 March n.y. · Unknown place · UCCL09047
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