|Millennium:||1st millennium BC|
|Centuries:||5th century BC – 4th century BC – 3rd century BC|
|Decades:||340s BC 330s BC 320s BC – 310s BC – 300s BC 290s BC 280s BC|
|Years:||321 BC 320 BC 319 BC – 318 BC – 317 BC 316 BC 315 BC|
|318 BC by topic|
|Gregorian calendar||318 BC|
|Ab urbe condita||436|
|Bahá'í calendar||−2161 – −2160|
|English Regnal year||N/A|
|Chinese calendar||壬寅年 (Water Tiger)
2379 or 2319
— to —
癸卯年 (Water Rabbit)
2380 or 2320
|Coptic calendar||−601 – −600|
|Ethiopian calendar||−325 – −324|
|- Vikram Samvat||−261 – −260|
|- Shaka Samvat||N/A|
|- Kali Yuga||2784–2785|
|Igbo calendar||−1317 – −1316|
|Iranian calendar||939 BP – 938 BP|
|Islamic calendar||968 BH – 967 BH|
|Minguo calendar||2229 before ROC
|Thai solar calendar||226|
|Wikimedia Commons has media related to 318 BC.|
Year 318 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Flaccinator and Venno (or, less frequently, year 436 Ab urbe condita). The denomination 318 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.
- Antigonus resolves to become lord of all Asia, and in conjunction with Cassander and Ptolemy. He enters into negotiations with Eumenes; but Eumenes remains faithful to the royal house. He raises an army and forms a coalition with the satraps of the eastern provinces. He then captures Babylon from Antigonus.
- Antigonus marches against Eumenes, so Eumenes withdraws east to join the satraps of the provinces beyond the Tigris River.
- Cassander, who has allied himself with Ptolemy and Antigonus, declares war on the regent, Polyperchon. Most of the Greek states support him, including Athens. Cassander further effects an alliance with Eurydice, the ambitious wife of King Philip III Arrhidaeus of Macedon.
- Although Polyperchon is initially successful in securing control of the Greek cities, whose freedom he proclaims, his fleet is destroyed by Antigonus.
- In a power struggle in Athens after the death of Antipater, Phocion is deposed as the ruler of Athens, convicted of treason, and executed by those Athenians hoping to restore democracy to the city. Shortly afterward, the Athenians decree a public burial and a statue in his honor.
- The state of Qin moves into the Sichuan basin, giving them control of that great food-producing plain.
- Aristoxenus, a Greek peripatetic philosopher, and writer on music and rhythm, and a pupil of Aristotle, writes a treatise on music called the "Elements of Harmony".