Cagayan Valley (Filipino: Lambak ng Cagayan, Ibanag: Tana' nak Cagayan, Ilokano: Tanap ti Cagayan, Itawis: Tanap yo Cagayan, Malaueg: Ga-dang yo Cagayan) is a region of thePhilippines (also designated as Region II or Region 02). It is composed of five provinces: Batanes, Cagayan, Isabela, Nueva Vizcaya, and Quirino. It has four cities: industrial center Cauayan City, its regional center Tuguegarao, its primary growth center and investment hub Ilagan City and its Premier City Santiago City.

Most of the region lies in a large valley in northeastern Luzon, between the Cordilleras and the Sierra Madre mountain ranges. The eponymous Cagayan River, the country's longest, runs through its center and flows out to the Luzon Strait in the north, at the town of Aparri, Cagayan. The Babuyan and Batanes island groups that lie in the Luzon Strait belong to the region.

Cagayan Valley is the second largest region of the Philippines in terms of land area.