| Marx to Thomas Allsop. 1 January |
| Engels to Johann Philipp Becker. 11 January |
| Marx to Wilhelm Liebknecht. 4 February |
| Marx to Thomas Allsop. 4 February |
| Marx to Wilhelm Liebknecht. 11 February |
| Marx to Sigmund Schott. 29 March |
| Marx to Valerian Smirnov. 29 March |
| Engels to Carl Hirsch. 3 April |
| Engels to Hermann Lopatin. 3 April |
| Marx to Thomas Allsop. 28 April |
| Engels to Wilhelm Bracke. 30 April |
| Marx to Carl Hirsch. 26 June |
| Marx to Sigmund Schott. 13 July |
| Marx to Sigmund Schott. 15 July |
| Engels to Valerian Smirnov. 16 July |
| Engels to Oscar Schmidt. 19 July |
| Engels to Philipp Pauli. 30 July |
| Engels to Pyotr Lavrov. 10 August |
| Marx to George Rivers. 24 August |
| Marx to Friedrich Adolph Sorge. 4 September |
| Engels to Friedrich Lessner. 12 September |
| Engels to Rudolf Engels. 12 September |
| Marx to Jenny Longuet. 16 September |
| Marx to Engels. 17 September |
| Marx to Jenny Marx. 17 September |
| Engels to Marx. 18 September |
| Marx to Engels. 18 September |
| Engels to Marx. 19 September
|
| Engels to Marx. 21 September |
| Marx to Engels. 24 September |
| Marx to Moritz Kaufmann. 3 October |
| Marx to Moritz Kaufmann. 10 October |
| Engels to Hermann Arnoldt. 21 October |
| Marx to an Unknown Correspondent. 4 November |
| Marx to Alfred Talandier. About 10 November- |
| Marx to Nikolai Danielson. 15 November |
| Engels to Ernst Dronke. 19 November |
| Marx to Nikolai Danielson. 28 November |
| Engels to Ernst Dronke. 29 November |
| Engels to Johann Philipp Becker. 12 December |