Sources: NIC
- Samuel L. Clemens to Bayard Taylor, 24 January 1877 · Hartford, Conn · UCCL01403
- Samuel L. Clemens to Bayard Taylor, 28 February 1878 · Hartford, Conn · UCCL01538
- Samuel L. Clemens to Bayard Taylor, 7 May 1878 · Heidelberg, Germany · UCCL01560
- Samuel L. Clemens to Bayard Taylor, 10 June 1878 · Heidelberg, Germany · UCCL01570
- Samuel L. Clemens to Bayard Taylor, 8 September 1878 · Geneva, Switzerland · UCCL01594
- Samuel L. Clemens to Bayard Taylor, 14 December 1878 · Munich, Germany · UCCL01614
- SLC to \"Jack,\" 23 June 1882 · Hartford, Conn · UCCL02225
- SLC to Julius John William Krueger, 22 July 1883 · Elmira, N.Y · UCCL01749
- SLC to Frederick J. Hall, 5 October 1885 · Hartford, Conn · UCCL03292
- OLC to Willard Fiske, April 1892 · Unknown place · UCCL11385
- SLC to Daniel Willard Fiske, 8? May 1892 · Florence, Italy · UCCL13444
- OLC to Daniel Willard Fiske, ?14 May 1892 · Florence, Italy · UCCL13445
- SLC to Willard Fiske, 29 May 1892 · Cadenabbia, Italy · UCCL11369
- SLC to Willard Fiske, 12 June 1892 · Bad Nauheim, Germany · UCCL11370
- OLC to Willard Fiske, 21 June 1892 · Bad Nauheim, Germany · UCCL11386
- OLC to Willard Fiske, 1 August 1892 · London, England · UCCL11387
- OLC to Willard Fiske, 26 September–17 June 1893 · Florence, Italy · UCCL11391
- OLC to Willard Fiske, 28 September 1892 · Florence, Italy · UCCL11388
- SLC to Willard Fiske, 5 November 1892 · Florence, Italy · UCCL11371
- SLC to Willard Fiske, 2 February 1893 · Florence, Italy · UCCL11372
- OLC to Willard Fiske, 17 June 1893 · Florence, Italy · UCCL11392
- OLC to Willard Fiske, 16 October 1893 · Homburg, Germany · UCCL11389
- Susy (Olivia Susan) Clemens to Willard Fiske, ca. 20 October 1893 · Paris, France · UCCL11398
- SLC to OLC, 28–31 October 1893 · Hartford, Conn · UCCL12386
- OLC to Willard Fiske, 11 November 1893 · Paris, France · UCCL11390
- OLC to Willard Fiske, 6 January 1894 · Paris, France · UCCL11393
- OLC to Willard Fiske, 17 September 1894 · Etretat, France · UCCL11394
- SLC to Willard Fiske, 15 July 1899 · Sanna, Sweden · UCCL11373
- SLC to Willard Fiske, 26 July 1900 · London, England · UCCL11382
- OLC to Willard Fiske, 17 September 1900 · London, England · UCCL11397
- SLC to Willard Fiske, 25 September 1900 · London, England · UCCL11383
- SLC to Willard Fiske, 25 September–6 October 1900 · London, England · UCCL11384
- SLC to Willard Fiske, 1 June 1903 · Unknown place · UCCL11381
- SLC to Willard Fiske, 1 June 1903 · New York, N.Y · UCCL11375
- SLC to Willard Fiske, 14 July 1903 · Elmira, N.Y · UCCL11376
- SLC to Willard Fiske, 19 July 1903 · Elmira, N.Y · UCCL11377
- SLC to Willard Fiske, 10 November 1903 · Florence, Italy · UCCL11378
- SLC to Willard Fiske, 14 November 1903 · Florence, Italy · UCCL11379
- SLC to Willard Fiske, 24 November 1903 · Florence, Italy · UCCL11380
- OLC to Willard Fiske, 18 December 1903 · Florence, Italy · UCCL11395
- OLC to Willard Fiske, 26 December 1903 · Florence, Italy · UCCL11396
- SLC per Isabel V. Lyon to Willard Fiske, 18 January 1904 · Florence, Italy · UCCL11374
- SLC to Michael Monahan, 4 February 1905 · New York, N.Y · UCCL06992
- SLC to Clara L. Clemens, 5 March 1907 · New York, N.Y · UCCL07671
- SLC to William D. Howells, 17 September n.y. · Unknown place · UCCL10183
- SLC to S. J. Medill, 2 October n.y. · Unknown place · UCCL04482
- SLC to John S. Hart, Unknown date, Hartford, Conn · UCCL05522
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