| Engels to Marx. 11 January |
| Marx to Engels. 21 January |
| Marx to Adolf Cluss. 21 January |
| Marx to Engels. 29 January |
| Marx to J C Mayer. After 3 Feb. |
| Engels to Marx. 11 February |
| Marx to Engels. 23 February |
| Engels to Marx. 10 March |
| Marx to Engels. 10 March |
| Marx to Bertalan Szemere. 10 March |
| Engels to Marx. 11 March |
| Marx to Engels. 22-23 March |
| Marx to Adolf Cluss. 25 March |
| Engels to Marx. 10 April |
| Engels to Joseph Weydemeyer. 12 April |
| Marx to Adolf Cluss. 17 April |
| Marx to Engels. 23 April |
| Marx to Engels. 26 April |
| Marx to Adolf Cluss. 26 April |
| Marx to Joseph Weydemeyer. 26 April |
| Engels to Marx. 26 April |
| Marx to Engels. 27 April |
| Engels to Marx. 27 April |
| Marx to Engels. 28 April |
| Engels to Marx. 20 May |
| Marx to Engels. 21 May |
| Engels to Marx. Before 28 May |
| Engels to Marx. 31 May |
| Engels to Marx. 1 June |
| Marx to Engels. 2 June |
| Engels to Marx. 6 June |
| Engels to Marx. 9 June |
| Marx to Engels. 14 June |
| Marx to Adolf Cluss. c. 14 June |
| Marx to Engels. 29 June |
| Marx to Engels. 8 July |
| Engels to Marx. 9 July |
| Marx to Engels . 18 July |
| Marx to Engels. 18 August |
| Engels to Marx. 24 August |
| Marx to James Grant, Editor of The Morning Advertiser. 31 August |
| Marx to Engels. 3 September |
| Marx to Engels. 7 September |
| Marx to Adolf Cluss. 15 September |
| Marx to Engels. 17 September |
| Engels to Marx. 19 September |
| Marx to Karl Blind. 26 September |
| Marx to Engels. 28 September |
| Engels to Marx. 29 September |
| Marx to Engels. 30 September |
| Marx to Joseph Weydemeyer. Early October |
| Marx to Adolf Cluss. 5 October |
| Marx to Engels. 8 October |
| Marx to Engels. 12 October |
| Marx to Karl Blind. 13 October |
| Marx to Adolf Cluss. 18 October |
| Marx to Engels. 28 October |
| Marx to Engels. 2 November |
| Marx to Engels. 6 November |
| Marx to Adolf Cluss. Mid-November |
| Marx to Engels. 21 November |
| Marx to Engels. 23 November |
| Marx to Engels. 2 December |
| Marx to Engels. c. 12 December |
| Marx to Engels. 14 December |