| Millennium: | 1st millennium BC |
|---|---|
| Centuries: | 2nd century BC – 1st century BC – 1st century |
| Decades: | 120s BC 110s BC 100s BC – 90s BC – 80s BC 70s BC 60s BC |
| Years: | 94 BC 93 BC 92 BC – 91 BC – 90 BC 89 BC 88 BC |
| 91 BC by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishments and disestablishments categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 91 BC |
| Ab urbe condita | 663 |
| Armenian calendar | N/A |
| Assyrian calendar | 4660 |
| Bahá'í calendar | -1934–-1933 |
| Bengali calendar | -683 |
| Berber calendar | 860 |
| English Regnal year | N/A |
| Buddhist calendar | 454 |
| Burmese calendar | -728 |
| Byzantine calendar | 5418–5419 |
| Chinese calendar | 己丑年 (2546/2606) — to —
庚寅年(2547/2607) |
| Coptic calendar | -374–-373 |
| Ethiopian calendar | -98–-97 |
| Hebrew calendar | 3670–3671 |
| Hindu calendars | |
| - Vikram Samvat | -34–-33 |
| - Shaka Samvat | N/A |
| - Kali Yuga | 3011–3012 |
| Holocene calendar | 9910 |
| Iranian calendar | 712 BP – 711 BP |
| Islamic calendar | 734 BH – 733 BH |
| Japanese calendar | |
| Korean calendar | 2243 |
| Minguo calendar | 2002 before ROC 民前2002年 |
| Thai solar calendar | 453 |
Year 91 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Philippus and Caesar (or, less frequently, year 663 Ab urbe condita). The denomination 91 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.