| Marx to Engels. 1 January |
| Engels to Marx. 3 January |
| Marx to Engels. 13 January |
| Engels to Marx. 17 January |
| Marx to Engels. 23 January |
| Engels to Marx. 25 January |
| Engels to Marx. 26 January |
| Marx to Engels. 28 January |
| Engels to Marx. 28 January |
| Marx to Engels. 29 January |
| Engels to Emil Blank. 4 February |
| Marx to Ludwig Kugelmann. 11 February |
| Marx to Engels. 13 February |
| Marx to Engels. 15 February |
| Marx to Paul and Laura Lafargue. 15 February |
| Engels to Marx. 17 February |
| Marx to Hermann Jung. 17 February |
| Engels to Marx. 21 February |
| Marx to Engels. 24 February |
| Engels to Marx. 25 February |
| Marx to Engels. 1 March |
| Marx to Engels. 2 March |
| Marx to Engels. 3 March |
| Engels to Marx. 3 March |
| Marx to Ludwig Kugelmann [Abstract]. 3 March |
| Marx to Heinrich Oberwinder. 3 March |
| Engels to Marx. 4 March |
| Marx to Engels [Abstract]. 5 March |
| Engels to Marx. 7 March |
| Marx to Engels. 14 March |
| Engels to Marx. 15 March |
| Engels to Marx. 18 March |
| Marx to Engels. 20 March |
| Engels to Marx. 21 March |
| Engels to Marx. 28 March |
| Marx to Engels. 29 March |
| Engels to Marx. 2 April |
| Engels to Marx. 4 April |
| Engels to Friedrich Lessner. 4 April |
| Marx to Engels. 5 April |
| Engels to Marx. 6 April |
| Marx to Engels. 7 April |
| Engels to Marx. 7 April |
| Marx to Engels. 8 April |
| Marx to John Malcolm Ludlow. 10 April |
| Engels to Marx. 14 April |
| Marx to Engels [Abstract]. 15 April |
| Engels to Marx. 16 April |
| Marx to Engels. 16 April |
| Engels to Marx. 19 April |
| Marx to Engels. 24 April |
| Engels to Marx. 25 April |
| Marx to Engels. 26 April |
| Marx to Eleanor Marx. 26 April |
| Marx to Engels. 1 May |
| Engels to Marx. 2 May |
| Engels to Marx. 2 May |
| Marx to Engels. 8 May |
| Engels to Marx. 11 May |
| Marx to Ludwig Kugelmann. 11 May |
| Engels to Hermann Engels. 13 May |
| Marx to Engels. 14 May |
| Engels to Marx. 19 May |
| Marx to Engels. 21 May |
| Engels to Marx. 23 May |
| Marx to P Le Neve Foster, Esq. 2 May |
| Marx to Paul Lafargue. 2 June |
| Marx to His Daughter Jenny. 2 June |
| Marx to His Daughter- Jenny. 10 June |
| Marx to Engels. 16 June |
| Engels to Marx. 22 June |
| Marx to Engels. 26 June |
| Engels to Marx. 27 June |
| Engels to Marx. 1 July |
| Engels to Elisabeth Engels. 1 July |
| Marx to Engels. 3 July |
| Marx to P St King. 3 July |
| Engels to Marx [Abstract]. 6 July |
| Marx to Francois Lafargue. 7 July |
| Engels to Jenny Marx (daughter). 9 July |
| Engels to Ludwig Kugelmann. 10 July |
| Marx to Francois Lafargue. 10 July |
| Marx to Engels. 14 July |
| Marx to Ludwig Kugelmann. 15 July |
| Engels to Hermann Engels. 15 July |
| Marx to Engels. 17 July |
| Engels to Marx. 18 July |
| Engels to Marx. 21 July |
| Marx to Engels. 22 July |
| Marx to Engels. 24 July |
| Engels to Marx. 25 July |
| Marx to Engels. 27 July |
| Engels to Ludwig Kugelmann. 28 July |
| Marx to Engels. 29 July |
| Engels to Marx. 30 July |
| Marx to Ludwig Kugelmann. 3 July |
| Marx to Engels. 2 August |
| Engels to Marx. 3 August |
| Marx to Engels. 4 August |
| Engels to Jenny Marx (daughter). 8 August |
| Marx to Engels [Abstract]. 10 August |
| Engels to Marx. 12 August |
| Marx to Hermann Jung. 1 August |
| Engels to Marx. 16 August |
| Engels to Marx. 16 August |
| Marx to Engels. 17 August |
| Marx to Engels [Abstract]. 18 August |
| Engels to Marx. 5 September |
| Marx to Engels [Abstract]. 25 September |
| Marx to Paul Lafargue. 25 September |
| Engels to Marx. 27 September |
| Marx to Engels. 30 September |
| Marx to Ludwig Kugelmann. 12 October |
| Marx to Paul and Laura Lafargue. 18 October |
| Engels to Marx. 22 October [abstract] |
| Marx to Engels. 23 October |
| Engels to Marx [Abstract]. 24 October |
| Marx to Engels. 30 October |
| Engels to Marx. 1 November |
| Marx to Engels. 6 November |
| Engels to Marx [Abstract]. 7 November |
| Marx to Engels. 12 November |
| Marx to Samuel Davenport. 12 November |
| Engels to Marx. 17 November |
| Marx to Engels [Abstract]. 18 November |
| Engels to Marx [Abstract]. 19 November |
| Marx to Engels [Abstract]. 26 November |
| Engels to Marx [Abstract]. 29 November |
| Marx to Kugelmann [Abstract]. 29 November |
| Marx to Engels. 4 December |
| Engels to Marx [Abstract]. 9 December |
| Marx to Engels [Abstract]. 10 December |
| Marx to Engels. 12 December |
| Engels to Marx. 15 December |
| Engels to Marx. 16 December |
| Marx to Engels. 17 December |