| Marx to Joseph Weydemeyer. 1 January |
| Engels to Marx. 6 January |
| Engels to Jenny Marx. 14 January |
| Marx to Joseph Weydemeyer. 16 January |
| Marx to Engels. 20 January |
| Engels to Marx. 22 January |
| Marx to Joseph Weydemeyer. 23 January |
| Engels to Joseph Weydemeyer. 23 January |
| Marx to Joseph Weydemeyer. 23 Jan/2 Feb |
| Marx to Engels. 24 January |
| Marx to Ferdinand Freiligrath. 26 January |
| Engels to Marx. 28 January |
| Engels to Marx. 29 January |
| Marx to Joseph Weydemeyer. 30 January |
| Engels to Joseph Weydemeyer. 30 January |
| Engels to Marx. 2 February |
| Marx to Engels. 4 February |
| Marx to Engels. 6 February |
| Marx to Joseph Weydemeyer. 13 February |
| Engels to Marx. 17 February |
| Marx to Engels. 18 February |
| Engels to Marx. 19 February |
| Engels to Joseph Weydemeyer. 19 February |
| Marx to Joseph Weydemeyer. 20 February |
| Marx to Engels. 23 February |
| Marx to Ferdinand Lassalle. 23 February |
| Marx to Engels. 27 February |
| Engels to Joseph Weydemeyer. 27 February |
| Engels to Marx. 2 March |
| Marx to Engels. 5 March |
| Marx to Joseph Weydemeyer. 5 March |
| Engels to Marx. 18 March |
| Marx to Joseph Weydemeyer. 25 March |
| Marx to Engels. 30 March |
| Engels to Marx. 1 April |
| Marx to Engels. 5 April |
| Marx to Engels. 14 April |
| Engels to Joseph Weydemeyer. 16 April |
| Engels to Marx. 20 April |
| Marx to Adolf Cluss. 22 April |
| Marx to Adolf Cluss. 23 April |
| Marx to Engels. 24 April |
| Engels to Marx. 25 April |
| Engels to Marx. 27 April |
| Engels to Marx. 29 April |
| Marx to Engels. 30 April |
| Marx to Joseph Weydemeyer. 30 April |
| Engels to Marx. 1 May |
| Engels to Marx. 4 May |
| Marx to Engels. 6 May |
| Engels to Marx. 7 May |
| Marx to Adolf Cluss. 7-15 May |
| Marx to Engels. 13 May |
| Engels to Marx. 19 May |
| Engels to Marx. 21 May |
| Engels to Marx. 22 May |
| Marx to Engels. 22 May |
| Engels to Marx. 24 May |
| Marx and Engels to Joseph Weydemeyer. 28 May |
| Marx to Jenny Marx. 11 June |
| Engels to Joseph Weydemeyer. 11 June |
| Marx to Adolf Cluss. Before 26 June |
| Engels to Marx. 30 June |
| Marx to Engels. 3 July |
| Engels to Marx. 6 July |
| Marx to Engels. 13 July |
| Engels to Marx. 15 July |
| Marx to Engels. 20 July |
| Marx to Adolf Cluss. 20 July |
| Engels to Marx. 22 July |
| Marx to Gottfried Kinkel. 22 June |
| Marx to Adolf Cluss. 30 July |
| Marx to Adolf Cluss. Early August |
| Marx to Engels. 2 August |
| Marx to Engels. 5 August |
| Engels to Marx. 6 August |
| Marx to Engels. 6 August |
| Engels to Marx. 9 August |
| Marx to Engels. 10 August |
| Engels to Marx. 16 August |
| Marx to Engels. 19 August |
| Marx to Heinrich Brockhaus. 19 August |
| Engels to Marx. 24 August |
| Marx to Engels. 27 August |
| Marx to Peter Imandt. 27 August |
| Marx to Engels. 30 August |
| Marx to Adolf Cluss. 30 August |
| Marx to Engels. 2 September |
| Marx to Adolf Cluss. 3 September |
| Marx to Adolf Cluss. After 5 Sept. |
| Engels to Marx. 7 September |
| Marx lo Engels. 8 September |
| Marx to Engels. 9 September |
| Engels to Marx. 14 September |
| Marx to Engels. 18 September |
| Engels to Marx. 20 September |
| Engels to Marx. 23 September |
| Marx to Engels. 23 September |
| Engels to Marx. 24 September |
| Marx to Engels. 28 September |
| Engels to Marx. After 28 Sept. |
| Engels to Marx. 4 October |
| Marx to Adolf Cluss. 5 October |
| Marx to Adolf Cluss. 8 October |
| Engels to Marx. 10 October |
| Marx to Engels. 12 October |
| Engels to Marx. 14 October |
| Engels to Marx. 18 October |
| Marx to A von Bruning. 18 October |
| Marx to Engels. 20 October |
| Engels to Marx. 22 October |
| Marx to Engels. 25 October |
| Marx to Engels. 26 October |
| Engels to Marx. 27 October |
| Marx to Engels. 27 October |
| Marx to Engels. 28 October |
| Engels to Marx. 28 October |
| Engels to Marx. 28 October |
| Engels to Marx. 31 October |
| Marx to Engels. 2 November |
| Marx to Engels. 4 November |
| Engels to Marx. 5-6 November |
| Marx to Engels. 10 November |
| Marx to Engels. 16 November |
| Marx to Engels. 19 November |
| Engels to Marie Blank. 22 November |
| Engels to Marx. 27 November |
| Engels to Marx. 29 November |
| Marx to Karl Eduard Vehse. End November |
| Marx to Engels. 3 December |
| Marx to Janos Bangya. 3 December |
| Marx to Adolf Cluss. 7 December |
| Marx to Engels. 14 December |
| Marx to Adolf Cluss. 14 December |
| Marx to Gustav Zerffi. 28 December |