Tuyên Quang province in the context of Lo River

A yamen (ya-men; traditional Chinese: 衙門; simplified Chinese: 衙门; pinyin: yámén; Wade–Giles: ya-men; Manchu: ᠶᠠᠮᡠᠨyamun) was the administrative office or residence of a local bureaucrat or mandarin in imperial China, Korea, and Vietnam. In some places, such as Kowloon Walled City, Hong Kong, it was named as almshouse. A yamen can also be any governmental office or body headed by a mandarin, at any level of government: the offices of one of the Six Ministries is a yamen, but so is a prefectural magistracy. The term has been widely used in China for centuries, but appeared in English during the Qing dynasty.

Yên Bái was a former province located in Northwest Vietnam. It shared borders with six provinces which are Hà Giang province, Lào Cai province, Lai Châu province, Sơn La province, Phú Thọ province, and Tuyên Quang province. The province covered an area of about 6,893 km (2,661 sq mi) and as of 2022 it had a population of 847,250 people.

Yên Bái's history is important under the French colony, particularly the subsequent "Yên Bái mutiny", an uprising of Vietnamese soldiers in the French colonial army on 10 February 1930 in collaboration with civilian supporters who were members of the Việt Nam Quốc Dân Đảng (VNQDD, the Vietnamese Nationalist Party).