| Marx to Engels. 3 January |
| Marx to Carl Siebel. 3 January |
| Marx to Carl Siebel. 3 January |
| Engels to Marx. 7 January |
| Marx to Engels. 8 January |
| Marx to Engels. 10 January |
| Marx to Ferdinand Lassalle, [Abstract]. 16 January |
| Marx to Engels. 18 January |
| Marx to Engels. 22 January |
| Marx to Ferdinand Lassalle. 28 January |
| Marx to Engels. 29 January |
| Marx to Engels. 31 January |
| Engels to Marx. 31 January |
| Marx to Engels. 2 February |
| Engels to Marx. 4 February |
| Engels to Marx. 6 February |
| Marx to Ferdinand Freiligrath. 7 February |
| Engels to Elisabeth Engels. 13 February |
| Marx to Engels. 14 February |
| Marx to Ferdinand Lassalle. 15 February |
| Marx to Engels, [Abstract]. 27 February |
| Engels to Elisabeth Engels. 27 February |
| Marx to Ferdinand Lassalle. 7 March |
| Marx to Antoinette Philips. 24 March |
| Marx to Carl Siebel. 28 March |
| Marx to Carl Siebel. 2 April |
| Marx to Antoinette Philips. 13 April |
| Marx to Lion Philips. 6 May |
| Marx to Engels. 7 May |
| Marx to Ferdinand Lassalle. 8 May |
| Marx to Engels. 10 May |
| Marx to Engels. 16 May |
| Marx to Ferdinand Lassalle. 29 May |
| Marx to Engels. 10 June |
| Marx to Ferdinand Lassalle. 11 June |
| Engels to Marx. 12 June |
| Marx to Engels. 19 June |
| Marx to Engels. 1 July |
| Engels to Marx. 3 July |
| Marx to Engels. 5 July |
| Marx to Engels. 12 July |
| Marx to Antoinette Philips. 17 July |
| Marx to Engels. 20 July |
| Marx to Ferdinand Lassalle. 22 July |
| Marx to Engels. 3 August |
| Marx to Antoinette Philips. 24 September |
| Marx to Engels. 28 September |
| Marx to Engels. 30 October |
| Marx to Engels. 6 November |
| Marx to Watteau. 10 November |
| Marx to Engels. 18 November |
| Marx to Engels. 20 November |
| Engels to Marx. 27 November |
| Engels to Marx. 2 December |
| Marx to Engels. 5 December |
| Marx to Engels. 9 December |
| Marx to Engels. 13 December |
| Marx to Engels. 19 December |
| Marx to Engels. 27 December |