Muang Phuan (Xieng Khouang, or Trấn Ninh (historical Vietnamese name of the province)) is a historical principality on the Xiangkhoang Plateau, which constitutes the modern territory of Xiangkhouang Province, Laos.

Among the Lao, Phuan, and Thai muang has a dual meaning of “city” or more broadly “country of” and xieng means “walled.”

The two terms are often used together for major city states under the Southeast Asian mandala model, thus Muang Xieng Khouang would be transcribed as the “Walled City/Country of the Phuan” (Khouang is a French corruption of Phuan).

The Xiangkhouang Plateau is semi-arid but has important iron ore resources and has been inhabited since the Bronze Age (the Plain of Jars is an important UNESCO archeological site).

The region is an important area for trade as it occupies the major passes along the Annamite Cordillera to access Vietnam and the coast.