Thucydides generally refers to Thucydides, son of Olorus, (circa 460-before 394 BC) a Greek historian. It may also refer to:
- 10137 Thucydides, a main-belt asteroid
- Thucydides, son of Melesias (5th century BC), prominent politician of ancient Athens
- Thucydides II, son of Melesias II (4th century), grandson of Thucydides, son of Melesias featured in Plato's Laches
- Thucydides Trap, where a rising power causes fear in an established power which escalates toward war