| Engels to Friedrich Adolph Sorge. 4 January |
| Engels to Rudolf Seiffert. 15/20 January |
| Marx to Nikolai Danielson. 18 January |
| Engels to Eugen Oswald. 29 January |
| Marx to Aristide Fanton. 1 February |
| Marx to Johann Philipp Becker. 11 February |
| Marx to Friedrich Bolte. 12 February |
| Engels to Wilhelm Liebknecht. 12 February |
| Engels to Maurice Lachatre. After 14 February |
| Engels to Natalie Liebknecht. 11 March |
| Engels to Eugen Oswald. 18 March |
| Engels to Friedrich Adolph Sorge. 20 March |
| Engels to Maurice Lachatre. After 21 March |
| Marx to Nikolai Danielson. 22 March |
| Engels to Friedrich Adolph Sorge. 22 March |
| Marx to Johann Philipp Becker. 7 April |
| Engels to Friedrich Adolph Sorge. 3 May |
| Marx to Maurice Lachatre. 12 May |
| Marx to Engels. 23 May |
| Marx to Hugo Heller. 23 May |
| Engels to Marx. 24 May |
| Marx to Engels. 25 May |
| Engels to Marx. 26 May |
| Engels to Marx. 30 May |
| Marx to Engels. 31 May |
| Engels to Friedrich Adolph Sorge. 14 June |
| Engels to August Bebel. 20 June |
| Engels to Walter Whitter. c. 24 June |
| Engels to Ludwig Kugelmann. 1 July |
| Marx to Juste Vernouillet. 10 July |
| Engels to Friedrich Adolph Sorge. 26 July |
| Marx to Nikolai Danielson. 12 August |
| Marx to Engels. 29 August |
| Engels to Marx. 30 August |
| Marx to Engels. 30 August |
| Engels to Marx. 3 September |
| Marx to Benjamin Le Moussu. c. 3 September |
| Marx to Engels. 9 September |
| Engels to John De Morgan. 18 September |
| Marx to Eugen Oswald. 20 September |
| Marx to Eugen Oswald. 24 September |
| Marx to Friedrich Adolph Sorge. 27 September |
| Engels to Friedrich Adolph Sorge. 25 November |
| Engels to Marx. 29 November |
| Marx to Engels. 30 November [abstract] |
| Engels to Marx. 5 December |
| Marx to Engels. 7 December |
| Engels to Marx. 10 December |
| Marx to Engels. 11 December |
| Marx to Thomas Allsop. 23 December |