Samhan or the Three Kingdoms of Korea (Korean: ; Hanja: ; RR: Samguk-sidae) refers to the three kingdoms of Goguryeo (, ), Baekje (, ), and Silla (, ). Goguryeo was later known as Goryeo (, ), from which the modern name Korea is derived. The Three Kingdoms period is defined as being from 57 BC to 668 AD (but there existed Gaya confederacy in the southern region of the Korean Peninsula and relatively large states like Okjeo, Buyeo, and Dongye in its northern part and Manchuria of modern China).

The three kingdoms occupied the entire peninsula of Korea and roughly half of Manchuria, located mostly in present-day China, along with smaller parts from present-day Russia. The kingdoms of Baekje and Silla dominated the southern half of the Korean Peninsula and Tamna (Jeju Island), whereas Goguryeo controlled the Liaodong Peninsula, Manchuria and the northern half of the Korean Peninsula. Baekje and Goguryeo shared founding myths which likely originated from Buyeo. Buddhism, which arrived in Korea in 3rd century CE from India via Tibet and China, became the state religion of all 3 constituents of the Three Kingdoms, starting with Gaya in 372 CE.In the 7th century, allied with China under the Tang dynasty, Silla unified the Korean Peninsula for the first time in Korean history, allowing for the first united Korean national identity. After the fall of Baekje and Goguryeo, the Tang dynasty established a short-lived military government to administer parts of the Korean Peninsula. However, as a result of the SillaTang War (670676 AD), Silla forces expelled the Protectorate armies from the peninsula in 676 AD. The following period is known as the Unified Silla or Later Silla (668935 AD).

Subsequently, Go of Balhae, a former Goguryeo general or chief of Sumo Mohe, founded Balhae in the former territory of Goguryeo after defeating the Tang dynasty at the Battle of Tianmenling.

The predecessor period, before the development of the full-fledged kingdoms, is sometimes called ProtoThree Kingdoms period.

Main primary sources for this period include Samguk sagi and Samguk yusa in Korea, and the "Eastern Barbarians" section () from the Book of Wei () of the Records of the Three Kingdoms in China.

The Goguryeo–Sui War were a series of invasions launched by the Sui dynasty of China against Goguryeo, one of the Three Kingdoms of Korea, between AD 598 and AD 614. It resulted in the defeat of the Sui and was one of the pivotal factors in the collapse of the dynasty, which led to its overthrow by the Tang dynasty in AD 618.