The Merino is a breed or group of breeds of domestic sheep, characterised by very fine soft wool. It was established in Spain near the end of the Middle Ages, and was for several centuries kept as a strict Spanish monopoly; exports of the breed were not allowed, and those who tried risked capital punishment. During the eighteenth century, flocks were sent to the courts of a number of European countries, including France, Hungary, the Netherlands, Prussia, Saxony and Sweden.

The Mesta was a powerful association protecting livestock owners and their animals in the Crown of Castile that was incorporated in the 13th century and was dissolved in 1836. Although best known for its organisation of the annual migration of transhumant sheep, particularly those of the Merino breed, the flocks and herds of all species of livestock in Castile and their owners were under the oversight of the Mesta, including both the transhumant and the sedentary ones. The transhumant sheep were generally owned in Old Castile and León, where they had their summer pastures, and they migrated to and from winter pastures of Extremadura and Andalusia according to the season.