SOYUZ 21
| Launched | 5 July 1976 |
| Flight ended | 23 August 1976 |
| Status | Decayed |
| Destination | Earth Landing |
| Launch site | Tyuratam Missile and Space Center, Kazakhstan (Also known as Baikonur Cosmodrome) |
| Owner | Commonwealth of Independent States (former USSR) |
| NORAD ID | 8934 |
| COSPAR ID | 1976-064A |
| Observing |
Launched alongside
SL-4 R/B