|Centuries:||3rd century – 4th century – 5th century|
|Decades:||310s 320s 330s – 340s – 350s 360s 370s|
|Years:||339 340 341 – 342 – 343 344 345|
|342 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1095|
|Bahá'í calendar||−1502 – −1501|
|English Regnal year||N/A|
|Chinese calendar||辛丑年 (Metal Ox)
3038 or 2978
— to —
壬寅年 (Water Tiger)
3039 or 2979
|- Vikram Samvat||398–399|
|- Shaka Samvat||264–265|
|- Kali Yuga||3443–3444|
|Igbo calendar||−658 – −657|
|Iranian calendar||280 BP – 279 BP|
|Islamic calendar||289 BH – 288 BH|
|Minguo calendar||1570 before ROC
|Thai solar calendar||885|
|Wikimedia Commons has media related to 342.|
Year 342 (CCCXLII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Claudius (or, less frequently, year 1095 Ab urbe condita). The denomination 342 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.
- A large earthquake strikes Cyprus.
- Goguryeo is invaded by Murong Huang of the Xianbei.
- Jin Kangdi succeeds his brother Jin Chengdi as emperor of China.
- Paul I, Patriarch of Constantinople, is deposed and replaced by Macedonius I.
- February 15 – The original Hagia Sophia is dedicated in Constantinople.
- July 26 – Jin Chengdi, emperor of the Jin Dynasty (b. 321)
- Paul of Thebes, Christian hermit (approximate date)