| Marx to Maxim Kovalevsky. 9 January |
| Engels to Wilhelm Liebknecht. 9 January |
| Engels to Hermann Engels. 9 January |
| Marx to Wilhelm Bracke. 21 January |
| Marx to Ferdinand Fleckles. 21 January |
| Marx to Wilhelm Alexander Freund. 21 January |
| Marx to Frederic Harrison. 21 January |
| Marx to Gabriel Deville. 23 January |
| Engels to Hermann Ramm. 25 January |
| Marx to Wilhelm Bracke. 14 February |
| Engels to Ida Pauli. 14 February |
| Engels to Marx. 23 February |
| Marx to Pyotr Lavrov. 24 February |
| Engels to Marx. 2 March |
| Marx to Engels. 3 March |
| Engels to Friedrich Lessner. 4 March |
| Marx to Engels. 5 March |
| Engels to Marx. 6 March |
| Marx to Engels. 7 March |
| Marx to Pyotr Lavrov. 16 March |
| Marx to Mrs Wollmann. 19 March |
| Marx to Pyotr Lavrov. 23 March |
| Engels to Johann Philipp Becker. 24 March |
| Engels to Philipp Pauli. 26 March |
| Marx to Pyotr Lavrov. 27 March |
| Marx to Pyotr Lavrov. 29 March |
| Marx to Wilhelm Bracke. 11 April |
| Engels to Wilhelm Liebknecht. 11 April |
| Marx to Philip Stephen King. 14 April |
| Marx to Pyotr Lavrov. 17 April |
| Marx to Thomas Allsop. 20 April |
| Marx to Wilhelm Bracke. 21 April |
| Marx to Pyotr Lavrov. 21 April |
| Engels to B Lindheimer. 21 April |
| Marx to Pyotr Lavrov. 23 April |
| Engels to Wilhelm Bracke. 24 April |
| Engels to B Lindheimer. 26 April |
| Engels to B Lindheimer. 3 or 4 May |
| Marx to Wilhelm Bracke. 26 July |
| Engels to Marx. 27 May |
| Marx to Engels. 31 May |
| Engels to Wilhelm Bracke. 25 June |
| Engels to Wilhelm Liebknecht. 2 July |
| Engels to Marx. 15 July |
|
Marx to Engels. 18 July |
| Engels to Marx. 19 July |
| Marx to Engels. 23 July |
| Engels to Marx. 24 July |
| Marx to Engels. 25 July |
| Engels to Franz Wiede. 25 July |
| Engels to Marx. 31 July |
| Engels to Natalie Liebknecht. 31 July |
| Engels to Wilhelm Liebknecht. 31 July |
|
Marx to Engels. 1 August |
| Marx to Wilhelm Bracke. 1 August |
| Marx to Engels. 8 August |
| Marx to Wilhelm Bracke. 8 August |
| Marx to Maltman Barry. 15 August |
| Marx to Engels. 17 August |
| Marx to Wilhelm Bracke. 18 August |
| Marx to Wilhelm Bracke. 24 August |
| Engels to Marx. 25 August |
| Marx to Nikolaus Delius. 25 August |
| Engels to Natalie Liebknecht. 4 September |
|
Marx to Friedrich Adolph Sorge. 27 September |
| Engels to Hermann Engels. 5 October |
| Engels to Ludwig Kugelmann. 12 October |
| Engels to Hermann Engels. 13 October |
|
Marx to Friedrich Adolph Sorge. 19 October |
| Marx to Wilhelm Bracke. 23 October |
| Marx to Sibylle Hess. 25 October |
| Marx to Sigmund Schott. 3 November |
|
Marx to Wilhelm Blos. 10 November |
| Engels to Ernst Dronke. 20 November |
| Marx to Sibylle Hess. 29 November |
| Engels to Marx. End of 1877 |