| Marx to Wilhelm Liebknecht. 7 January |
| Marx to Wilhelm Liebknecht. 9 January |
| Marx to Max Oppenheim. 20 January |
| Marx to Maurice Lachatre. 30 January |
| Marx to Juste Vernouillet. 3 February |
| Marx to Pyotr Lavrov. 11 February |
| Marx to Engels. Feb/March |
| Engels to Hermann Ramm. 18 March |
| Engels to August Bebel. 18-28 March |
| Engels to Rudolf Engels. 22 March |
| Marx to Wilhelm Bracke. 5 May |
| Marx to Pyotr Lavrov. 8 May |
| Engels to Eugen Oswald. 8 May |
| Marx to Jenny Marx. 10 May |
| Engels to Patrick John Coleman. 20 May |
| Engels to A Goopy. 14 June |
| Marx to Pyotr Lavrov. 18 June |
| Marx to Z. 12 July |
| Marx to Edwards. 14 July |
| Marx to Engels. 21 August |
| Marx to Max Oppenheim. 1 September |
| Marx to Max Oppenheim. 6 September |
| Marx to Engels. 8 September |
| Marx to Max Oppenheim. 9 September |
| Marx to Hermann Schumacher. 21 September |
| Engels to Pyotr Lavrov. 24 September |
| Marx to Peter Imandt. 27 September |
| Marx to Bernhard Kraus. 30 September |
| Marx to Pyotr Lavrov. 8 October |
| Engels to Wilhelm Bracke. 11 October |
| Engels to August Bebel. 12 October |
| Engels to August Bebel. 15 October |
| Marx to Bernhard Kraus. 20 October |
| Engels to Philipp Pauli. 8 November |
| Engels to Philipp Pauli. 9 November |
| Engels to Rudolf Engels. 9 November |
| Engels to Pyotr Lavrov. 17 November |
| Engels to Paul Kersten. 24 November |
| Marx to Morel. Autumn |
| Marx to Pyotr Lavrov. 3 December |
| Engels to Walery Wroblewski. 4 December |
| Engels to Friedrich Lessner. 16 December |
| Marx to Pyotr Lavrov. 17 December |