| Marx to Eduard von Muller-Tellering. 1 January |
| Marx to Joseph Weydemeyer. 8 January |
| Marx to Ferdinand Freiligrath. 11 January |
| Marx to Joseph Weydemeyer. 4 February |
| Marx to Louis Bauer. 5 February |
| Engels to Eduard von Muller-Tellering. 7 February |
| Engels to Julius Schuberth, Theodor Hagen and Stephen Naut. 4 March |
| Marx to Eduard von Muller-Tellering. 12 March |
| Marx to Joseph Weydemeyer. 9 April |
| Engels to Julius Schuberth. c. 11 April |
| Engels to Joseph Weydemeyer. 22 April |
| Engels to Joseph Weydemeyer. 25 April |
| Engels and Marx to Francois Pardigon. 6 May |
| Engels to Theodor Schuster. 13 May |
| Engels to Joseph Weydemeyer. 8 June |
| Marx to Heinrich Burgers. 25 June |
| Marx to Joseph Weydemeyer. 27 June |
| Marx to Karl Blind. 17 July |
| Marx to Joseph Weydemeyer. 29 October |
| Marx to Engels. 19 November |
| Marx to Engels. 23 November |
| Engels to Marx. 25 November |
| Marx to Engels. 2 December |
| Marx to Hermann Becker. 2 December |
| Engels to Emil Blank. 3 December |
| Engels to Marx. 17 December |