| Horst Rittner | |
| Full Name: | Horst Robert Rittner |
| Country: | Germany |
| Birth Date: | 16 July 1930 |
| Birth Place: | Breslau, Germany (today Wrocław, Poland) |
| ICCF Grandmaster (1961) | |
| Iccfworldchampion: | 1968–1971 |
Horst Robert Rittner (16 July 1930 – 14 June 2021) was a German correspondence chess Grandmaster. He was born in Breslau, Weimar Germany, and was the sixth ICCF World Champion, between 1968 and 1971. He also edited the German magazine Schach.