Campoo (really called Campoo-Los Valles) is a comarca of Cantabria (Spain) located in the High Ebro, with a surface little bigger than 1,000 km², and including the municipalities of Hermandad de Campoo de Suso, Campoo de Enmedio, Campoo de Yuso, Valdeolea, Valdeprado del Río, Valderredible, Reinosa, Las Rozas de Valdearroyo, Santiurde de Reinosa, Pesquera, and San Miguel de Aguayo. Their inhabitants are called Campurrians (Campurrianos, in Spanish). Its highest elevation is the Cuchillón peak (2,225 m above sea level), and the lowest is Pesquera (560 m), with the capital, Reinosa at 850 m.

Originally, as it is gathered in the Book of Merindades of Castile (from circa 1352), the Merindad of Aguilar de Campoo comprised municipalities of the south of present Cantabria, as well as of northern Province of Palencia and Burgos, with its capital being the Palentine Aguilar de Campoo, ancient capital also of the vast Marquesse of Aguilar de Campoo. Later the capital was moved to Reinosa, which still has this status. The "Palentine Campoo" was left, after the provincial division, with Aguilar as the most important township, and included nowadays into the large comarca of Palentine Mountains.

Campoo is placed in a transition zone between the Eurosiberian and the Mediterranean regions of the Iberian Peninsula (see Forests of the Iberian Peninsula). Its climate is generally cold and humid, influenced by the Continental (as it is open to the Meseta) and Oceanic climates, the last one smoothed by the Ísar ranges and the Cantabrian Mountains. This climate combination can be observed in very cold winters and gentle summers, with no extreme temperatures. With Reinosa in the middle, we can find a more Mediterranean zone, comprising Valderredible and Valdeolea, and to the North, near the end of the Besaya River, the climate becomes clearly Oceanic.

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