Jin (, Old Chinese: *tsi[n]-s), originally known as Tang (唐), was a major state during the middle part of the Zhou dynasty, based near the centre of what was then China, on the lands attributed to the legendary Xia dynasty: the southern part of modern Shanxi. Although it grew in power during the Spring and Autumn period, its aristocratic structure saw it break apart when the duke lost power to his nobles. In 403 BC, the Zhou court recognized Jin's three successor states: Han, Zhao, and Wei. The Partition of Jin marks the end of the Spring and Autumn Period and the beginning of the Warring States period.
Jin was located in the lower Fen River drainage basin on the Shanxi plateau. To the north were the Xirong and Beidi peoples. To the west were the Lüliang Mountains and then the Loess Plateau of northern Shaanxi. To the southwest the Fen River turns west to join the south-flowing part of the Yellow River which soon leads to the Guanzhong, an area of the Wei River Valley that was the heartland of the Western Zhou and later of the Qin. To the south are the Zhongtiao Mountains and then the east-west valley of the Yellow River which was the main route to the Wei Valley to the west. To the east were the Taihang Mountains and then the North China Plain. This location gave ambitious Jin dukes the opportunity to move north to conquer and absorb the Xirong tribes, move southwest and fight Qin, and move southeast to absorb the many smaller Zhou states.
Also important to the region were the large states of Chu to the south in the Yangtze and Huai River regions and Qi to the east in Shandong.
Jin had multiple capitals. The first capital of Jin was Tang (唐). The capital was later moved to E (鄂), then Jiang (絳), then Xintian (新田). From 746 to 677, Quwo (曲沃) was the capital of a fragment of Jin.
When the Zhou Dynasty was founded, the conquered lands were given to Zhou relatives and ministers as hereditary fiefs. King Cheng of Zhou, the second Zhou king, gave the land called Tang (唐), west of modern Yicheng County in Shanxi, to his younger brother, Tang Shuyu (唐叔虞) with the rank of a marquis.