Cagayán, situated in the northeastern part of Luzon Island in the Philippines, is a province within the Cagayan Valley region. It encompasses the Babuyan Islands to the north and shares borders with Ilocos Norte and Apayao to the west, as well as Kalinga and Isabela to the south. The provincial capital is Tuguegarao City.

During the Spanish Colonial Period, Cagayán was known as La Provincia de Cagayan, covering the entire Cagayan Valley, including present-day Isabela, Quirino, Nueva Vizcaya, Batanes, and parts of Kalinga and Apayao. The historical capital was Nueva Segovia, serving as the seat of the Diocese of Nueva Segovia. Today, only 9,295.75 square kilometers (3,589.11 sq mi) remain of its original vastness. Despite this, the entire region is still commonly referred to as Cagayan Valley.