| Centuries: | 6th century · 7th century · 8th century |
| Decades: | 630s 640s 650s 660s 670s 680s 690s |
| Years: | 663 664 665 666 667 668 669 |
| 666 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 666 DCLXVI |
| Ab urbe condita | 1419 |
| Armenian calendar | 115 ԹՎ ՃԺԵ |
| Bahá'í calendar | -1178 – -1177 |
| Bengali calendar | 73 |
| Berber calendar | 1616 |
| Buddhist calendar | 1210 |
| Burmese calendar | 28 |
| Byzantine calendar | 6174 – 6175 |
| Chinese calendar | 乙丑年十一月二十日 (3302/3362-11-20) — to —
丙寅年十二月初一日(3303/3363-12-1) |
| Coptic calendar | 382 – 383 |
| Ethiopian calendar | 658 – 659 |
| Hebrew calendar | 4426 – 4427 |
| Hindu calendars | |
| - Bikram Samwat | 722 – 723 |
| - Shaka Samvat | 588 – 589 |
| - Kali Yuga | 3767 – 3768 |
| Holocene calendar | 10666 |
| Iranian calendar | 44 – 45 |
| Islamic calendar | 45 – 46 |
| Japanese calendar | |
| Korean calendar | 2999 |
| Thai solar calendar | 1209 |