|Millennium:||1st millennium BC|
|Centuries:||2nd century BC – 1st century BC – 1st century|
|Decades:||90s BC 80s BC 70s BC – 60s BC – 50s BC 40s BC 30s BC|
|Years:||69 BC 68 BC 67 BC – 66 BC – 65 BC 64 BC 63 BC|
|66 BC by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishments and disestablishments categories|
|Establishments – Disestablishments|
|Gregorian calendar||66 BC|
|Ab urbe condita||688|
|Bahá'í calendar||−1909 – −1908|
|English Regnal year||N/A|
|Chinese calendar||甲寅年 (Wood Tiger)
2631 or 2571
— to —
乙卯年 (Wood Rabbit)
2632 or 2572
|Coptic calendar||−349 – −348|
|Ethiopian calendar||−73 – −72|
|- Vikram Samvat||−9 – −8|
|- Shaka Samvat||N/A|
|- Kali Yuga||3036–3037|
|Igbo calendar||−1065 – −1064|
|Iranian calendar||687 BP – 686 BP|
|Islamic calendar||708 BH – 707 BH|
|Minguo calendar||1977 before ROC
|Thai solar calendar||478|
|Wikimedia Commons has media related to 66 BC.|
Year 66 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Lepidus and Tullus (or, less frequently, year 688 Ab urbe condita). The denomination 66 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.
- Consuls: Manius Aemilius Lepidus and Lucius Volcatius Tullus.
- Catiline accused of conspiring against the Roman Republic with Autronius and the younger Sulla (also in 63 during the consulship of Cicero).
- The alliance between Mithridates VI of Pontus and Tigranes II of Armenia is broken.
- Tigranes II is forced to surrender, by a payment of 6,000 talents, and is reinstated by Pompey as a "friend of the Roman people" to hold Armenia as a buffer zone.
- Battle of the Lycus: Pompey the Great decisively defeats Mithridates VI, effectively ending the Third Mithridatic War.
- Gaius Antonius elected Roman praetor.
- The lex Manilia, supported by Cicero gives Pompey command over all of Asia.
- Cicero becomes praetor in Rome.
- Licinius Macer, Roman annalist