Cagayan Valley is the large mass of land in the northeastern region of Luzon, comprising today the provinces of Cagayan, Isabela, Nueva Vizcaya, Quirino, and the Batanes group of islands. It is bounded to the west by the Cordillera Mountain Range, to the east by the Sierra Madre Mountain Range, to the south by the Caraballo Mountains, and to the north by the Luzon Strait, where the waters of the Pacific Ocean in the east and the South China Sea in the west, meet.
Cagayan Valley, contains two landlocked provinces, Quirino and Nueva Vizcaya. The two provinces are relatively small in size (3057 km2 for Quirino, 4081 km2 for Nueva Vizcaya) and population (147,000 and 365,000, respectively, by the 2000 census). They are ruggedly mountainous and heavily forested. Nueva Vizcaya is the remnant of the southern province created when Cagayan Province was divided in two in 1839. They are ethnically and linguistically diverse, with a substrate of Agtas, Negritos who are food-gatherers with no fixed abodes, overlaid by Ilongots and others in a number of tribes, some of whom were fierce head-hunters (they have given up the practice), with the latest but largest element of the population being Ilokano.