The name "Three Kingdoms" was used in the titles of the histories Samguk Sagi (12th century) and Samguk Yusa (13th century) therefore everyone should not be confused with the earlier Chinese Three Kingdoms.

The Three Kingdoms of Korea refer to the ancient Korean kingdoms of Goguryeo, Baekje and Silla, which dominated the Korean peninsula and parts of Manchuria for much of the 1st millennium CE. The Three Kingdoms period ran from 57 BCE until Silla's triumph over Goguryeo in 668, which marked the beginning of the North and South States period of Unified Silla in the South and Balhae in the North. The earlier part of this period, before the three states developed into full-fledged kingdoms, is sometimes called Proto-Three Kingdoms of Korea.

Map of the Three Kingdom of Korea in the end of 5th century

The three city-states were founded soon after the fall of Gojoseon, and gradually conquered and absorbed various other small states and confederacies. After the fall of Gojoseon, the Han dynasty established four commanderies in northern parts of the Korean peninsula. Three fell quickly to the Samhan, and the last was destroyed by Goguryeo in 313.

Baekje and Silla expanded within the Samhan confederacies, and Goguryeo conquered neighboring Buyeo, Okjeo, Dongye, and other statelets in northern Korea and Manchuria. The three became full-fledged kingdoms by around 300 CE.

All three kingdoms shared a similar culture and language. Their original religions appear to have been shamanistic, but they were increasingly influenced by Chinese culture, particularly Confucianism and Taoism. In the 4th century, Buddhism was introduced to the peninsula and spread rapidly, briefly becoming the official religion of all three kingdoms.