| Marx to Engels. after 11 Jan. |
| Marx to Bertalan Szemere. 12 January |
| Marx to Engels. 25 January |
| Engels to Marx. 26 January |
| Marx to Engels. 28 January |
| Marx to Ferdinand Lassalle. 30 January |
| Engels to Marx. 31 January |
| Marx to Engels. 31 January |
| Marx to Bertalan Szemere. 31 January |
| Engels to Marx. 1 February |
| Engels to Marx. 2 February |
| Marx to Engels. 3 February |
| Marx to Joachim Lelewel. 3 February |
| Engels to Marx. 4 February |
| Marx to Engels. 4 February |
| Marx to Franz Duncker. 6 February |
| Engels to Marx. 7 February |
| Marx to Engels. 7 February |
| Marx to Ferdinand Freiligrath. 8 February |
| Marx to Engels. 9 February |
| Engels to Marx. 9 February |
| Engels to Marx. 12 February |
| Marx to J M Weber. 13 February |
| Marx to Engels. 13 February |
| Marx to Engels. 14 February |
| Marx to Engels. 15 February |
| Engels to Franz Duncker. 20 February |
| Engels to Ferdinand Lassalle. 20 February |
| Marx to J M Weber. 21 February |
| Marx to Ferdinand Freiligrath. 23 February |
| Marx to Ferdinand Lassalle. 23 February |
| Marx to J M Weber. 24 February |
| Marx to Wilhelm Liebknecht. 27 February |
| Marx to Karl Schapper. 27 February |
| Marx to Muzembini. 27 February |
| Marx to Ferdinand Freiligrath. 29 February |
| Marx to Ferdinand Lassalle. 3 March |
| Marx to J M Weber. 3 March |
| Marx to Collet Dobson Collet. 7 March |
| Marx to Bertalan Szemere. 13 March |
| Marx to Lucien Jottrand. 13 March |
| Engels to Ferdinand Lassalle. 15 March |
| Marx to J M Weber. 27 March |
| Marx to Bertalan Szemere. 4 April |
| Engels to Marx. 8 April |
| Marx to Engels. 9 April |
| Marx to Johann Philipp Becker. 9 April |
| Marx to Ferdinand Lassalle. 9 April |
| Marx to Georg Lommel. 9 April |
| Engels to Emil Engels. 11 April |
| Marx to Engels. 12 April |
| Marx to J M Weber. 13 April |
| Marx to Engels. 16 April |
| Marx to Mor Perczel. 16 April |
| Marx to Engels. 17 April |
| Engels to Gottfried Ermen. 19 April |
| Marx to J M Weber. 21 April |
| Marx to Engels. 24 April |
| Marx to Ceorg Rheinlander. 24 April |
| Marx to Ferdinand Lassalle. 24 April |
| Marx to J M Weber. 24 April |
| Marx to Engels. 7 May |
| Engels to Marx. 7 May |
| Marx to Engels. 8 May |
| Marx to Eduard Fischel. 8 May |
| Engels to Marx. 10 May |
| Engels to Marx. 11 May |
| Marx to Carl Siebel. 15 May |
| Marx to Engels. 28 May |
| Engels to Marx. 31 May |
| Marx to Eduard Fischel. 1 June |
| Marx to Ferdinand Lassalle. About 2 June |
| Marx to Engels. 2 June |
| Marx to Bertalan Szemere. 2 June |
| Marx to Engels. 14 June |
| Marx to Engels. 16 June |
| Engels to Marx. 20 June |
| Marx to Johann Philipp Becker. 23 June |
| Engels to Marx. About 25 June |
| Marx to Engels. 25 June |
| Marx to Engels. 26 June |
| Engels to Marx. 26 June |
| Engels to Marx. 27 June |
| Marx to Engels. 28 June |
| Engels to Marx. After 28 June |
| Marx to Engels. 9 July |
| Marx to Engels. 17 July |
| Marx to Engels. 21 July |
| Engels to Marx. About 23 July |
| Marx to Engels. 25 July |
| Marx to Engels. 29 July |
| Engels to Marx. 1 August |
| Marx to J M Weber. 2 August |
| Marx to Engels. 4 August |
| Engels to Jenny Marx. 15 August |
| Marx to J M Weber. 20 August |
| Marx to Bertalan Szemere. 21 August |
| Marx to Engels. 27 August |
| Marx to Engels. 29 August |
| Marx to Engels. 1 September |
| Marx to Engels. After 2 Sept. |
| Marx to Ferdinand Lassalle. 7 September |
| Marx to Engels. 13 September |
| Marx to Engels. 15 September |
| Engels to Marx. 15 September |
| Marx to Ferdinand Lassalle. 15 September |
| Marx to Ferdinand Lassalle. 15 September |
| Marx to Engels. 20 September |
| Marx to Engels. 25 September |
| Engels to Marx. 1 October |
| Marx to Engels. 2 October |
| Marx to Ferdinand Lassalle. 2 October |
| Engels to Marx. 5 October |
| Marx to Engels. 11 October |
| Marx to Ferdinand Lassalle. 23 October |
| Marx to Engels. 25 October |
| Marx to Engels. 5 November |
| Marx to Ferdinand Lassalle. 5 November |
| Marx to Engels. 13 November |
| Marx to Engels. 14 November |
| Marx to Engels. 21 November |
| Marx to Bertalan Szemere. 22 November |
| Marx to Bertalan Szemere. 22 November |
| Marx to Engels. 23 November |
| Marx to Franz Duncker. 24 November |
| Marx to Engels. 26 November |
| Marx to Engels. 28 November |
| Engels to Marx. 3 December |
| Engels to Marx. 5 December |
| Marx to Engels. 5 December |
| Marx to Engels. 6 December |
| Marx to Engels. 12 December |
| Engels to Marx. 18 December |
| Marx to Engels. 18 December |
| Engels to Marx. 19 December |
| Marx to Engels. 19 December |
| Marx to Engels. 23 December |
| Marx to Engels. 26 December |
| Marx to Engels. 27 December |