Samguk sagi (Korean: 삼국사기; Hanja: 三國史記; lit. History of the Three Kingdoms) is a historical record of the Three Kingdoms of Korea: Goguryeo, Baekje, and Silla. Completed in 1145, it is well-known in Korea as the oldest surviving chronicle of Korean history.

The Samguk sagi is written in Classical Chinese, the written language of the literati of ancient Korea. Its compilation was ordered by King Injong of Goryeo (r. 1122–1146) and undertaken by a government official and historian named Kim Pusik with his team of junior scholars. The document has been digitized by the National Institute of Korean History and is available online with Modern Korean translation in Hangul.

Samguk sagi is critical to the study of Korean history during the Three Kingdoms and Unified Silla periods. Not only because this work, and its Buddhist counterpart Samguk yusa, are the only remaining Korean sources for the period, but also because the Samguk sagi contains a large amount of information and details. For example, the translation tables given in Books 35 and 36 have been used for a tentative reconstruction of the former Goguryeo language.

There were various motivating factors behind the compilation of the Samguk sagi in the 12th century. These may roughly be categorized as ideological and political. The ideological factors are made manifest in the work's preface, written by Kim Busik, where the civil historian states,

"Of today's scholars and high-ranking officials, there are those who are well-versed and can discuss in detail the Five Classics and the other philosophical treatises... as well as the histories of Qin and Han, but as to the events of our country, they are utterly ignorant from beginning to end. This is truly lamentable."

The Samguk sagi was written on the basis of the Gu Samguksa (舊三國史, Old History of the Three Kingdoms), and other earlier historical records such as the Hwarang Segi (花郞世記, Annals of Hwarang), most of which are no longer extant.

Concerning external sources, no references are made to the Japanese chronicles, like the Kojiki (712) or the Nihon Shoki (720), chronicles of Japan. It is possible Kim Busik was ignorant of them or scorned to quote a Japanese source. In contrast, he lifts generously from the Chinese dynastic chronicles and even unofficial Chinese records, most prominently the Records of the Three Kingdoms (280–290), Book of Wei (554), Book of Jin (648), Old Book of Tang (945), New Book of Tang (1060), and the Zizhi Tongjian (1084).

The Samguk sagi is divided into 50 books. Originally, each of them was written on a scroll (권; 卷). They are listed as follows: