| Engels to Wilhelm Liebknecht. 2 January |
| Engels to Wilhelm Liebknecht. 3 January |
| Marx to Maltman Barry. 7 January |
| Engels to Carlo Terzaghi - First Version. After 6 January |
| Engels to Carlo Terzaghi - Second Version. 14-15 January |
| Engels to Wilhelm Liebknecht. 18 January |
| Engels to Pyotr Lavrov. 19 January |
| Engels to Paul Lafargue. 19 January |
| Marx to Hermann Jung. 19 January |
| Engels to Theodor Cuno. 24 January |
| Engels to Carlo Terzaghi. 29 January |
| Marx to Ferdinand Jozewicz. 1 February |
| Marx to Hermann Jung. 1 February |
| Marx to Mauriee Laehatre and Juste Vernouillet. 9 February |
| Marx to Adolphe Hubert. 12 February |
| Marx to Asher & Co. 13 February |
| Engels to Wilhelm Liebknecht. 15 February |
| Engels to Johann Philipp Becker. 16 February |
| Engels to Giuseppe Benedetti. 18 February |
| Engels to William Burrs. 22 February |
| Marx to Ferdinand Jozewiez. 24 February |
| Marx to Hermann Jung. 26 February |
| Marx to Laura Lafargue. 28 February |
| Engels to Sigismund Borkheim. Early March |
| Engels to Louis Pio. 7 March |
| Marx to Hermann Jung. 7 March |
| Marx to Friedrich Adolph Sorge. 8 March |
| Marx to Emile Eudes. 9 March |
| Engels to Paul Lafargue. 11 March |
| Engels to Laura Lafargue. 11 March |
| Engels to Louis Pio. Mid-March |
| Marx to Friedrich Adolph Sorge. 15 March |
| Engels to Friedrich Adolph Sorge. 17 March |
| Marx to Maurice Lachatre. 18 March |
| Engels to Cesare Bert. 21 March |
| Marx to Paul Lafargue. 21 March |
| Engels to Carlo Terzaghi. 21 March |
| Marx to Edouard Vaillant. 4 April |
| Engels to Cennaro Bovio. 16 April |
| Engels to Theodor Cuno. 22-23 April |
| Engels to Wilhelm Liebknecht. 23 April |
| Marx to Johann Georg Eccarius. 3 May |
| Engels to Wilhelm Liebknecht. 7 May |
| Engels to Theodor Cuno. 7-8 May |
| Engels to Johann Philipp Becker. 9 May |
| Engels to Wilhelm Liebknecht. 15-22 May |
| Marx to Friedrich Adolph Sorge. 23 May |
| Marx to Edouard Vaillant. 24 May |
| Marx to Friedrich Adolph Sorge. 27 May |
| Engels to Wilhelm Liebknecht. 27-28 May |
| Marx to Nikolai Danielson. 28 May |
| Marx to Cesar De Paepe. 28 May |
| Marx to Friedrich Adolph Sorge. 29 May |
| Engels to Wilhelm Liebknecht. 5-6 June |
| Engels to Molesworth. After 5 June |
| Engels to Cesare Bert. 7 June |
| Engels to Theodor Cuno. 10 June |
| Engels to Johann Philipp Becker. 14 June |
| Engels to Carlo Cafiero. 14 June |
| Marx to Friedrich Adolph Sorge. 21 June |
| Marx to Octave van Suetendael. 21 June |
| Engels to Adolf Hepner. 2 July |
| Engels to Th. Smart & Co. After 3 July |
| Engels to Theodor Cuno. 5 July |
| Marx to Ludwig Kugelmann. 9 July |
| Engels to Adolf Hepner. 9 July |
| Engels to Ugo Bartorelli. 18 July |
| Marx to Ludwig Kugelmann. 23 July |
| Marx to Ludwig Kugelmann. 29 July |
| Marx to Hermann Jung. End of July |
| Engels to Adolf Hepner. 4 August |
| Engels to Theodor Cuno. 4 August |
| Engels to Johann Philipp Becker. 5 August |
| Engels to Walery Wroblewski. 7 August |
| Marx to Nikolai Danielson. 15 August |
| Marx to Juste Vernouillet. 15 August |
| Engels to E Glaser de Willebrord. 19 August |
| Engels to Wilhelm Liebknecht. 24 August |
| Marx to Ludwig Kugelmann. 26 August |
| Engels to Hermann Jung. c. 1 September |
| Engels to Maltman Barry. 15 September |
| Engels to Friedrich Adolph Sorge. 21 September |
| Engels to Hermann Jung. 1 October |
| Marx to P van der Willigen. 4 October |
| Engels to Friedrich Adolph Sorge. 5 October |
| Marx to Maurice Lachatre. 12 October |
| Marx to Hermann Jung. 14 October |
| Engels to Friedrich Lessner. 16 October |
| Engels to Theodor Cuno. 29 October |
| Engels to Jenny Longuet. 30 October |
| Engels to Friedrich Adolph Sorge. 2 November |
| Engels to Friedrich Adolph Sorge. 16 November |
| Engels to Jenny Longuet. 19 November |
| Marx to Nikolai Danielson. 25 November |
| Engels to Friedrich Adolph Sorge. 7 December |
| Marx to Nikolai Danielson. 12 December |
| Engels to Friedrich Adolph Sorge. 14 December |
| Marx to Friedrich Adolph Sorge. 21 December |
| Marx to William Riley. 23 December |
| Engels to Adolf Hepner. 30 December |