Cagayan Valley is the large mass of land in the northeastern region of Luzon, comprising today the provinces of Cagayan, Isabela, Nueva Vizcayaand Quirino. It is bounded to the west by the Cordillera Mountain Range, to the east by the Sierra Madre Mountain Range, and bounded by theBabuyan Island, 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. Both are relatively small in size (3057 km² for Quirino, 4081 km²for 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.

Nueva Vizcaya comprises 15 towns; Bayombong is the capital. Agriculture in both has until recently consisted of slash-and-burn cultivation of corn and maize, though more stable cultivation of vegetables and fruits is becoming established. They produce logs and are trying to manage their forest resources so that production can be sustained indefinitely. They have deposits of gold, silver, copper, iron. Nueva Vizcaya has sand and clay.

Archaeology indicates that the Cagayan Valley has been inhabited for half a million years, though no human remains of any such antiquity have yet appeared. The earliest inhabitants are the Agta, or Atta, food-gatherers who roam the forests without fixed abodes. A large tract of land has lately been returned to them. The bulk of the population are of Malay origin. For centuries before the coming of the Spanish, the inhabitants traded with Indians, Malays, Chinese, and Japanese. In the nineteenth century the prosperity found in tobacco cultivation caused many Ilokano to settle here. Tobacco is still a major factor in the economy of Cagayan, though a special economic zone and free port has been created to strengthen and diversify the provincial economy.

During Spanish times Cagayan Valley had a larger territory than what it has today. It included the territories of the above-mentioned provinces and the eastern parts of the Cordillera provinces ofApayao, Kalinga, Ifugao and Benguet. As the historian and missionary Jose Burgues, said, "The old Cagayan Valley comprises the province of Cagayan, Isabela and Nueva Vizcaya as well as the military Districts of Apayao, Itaves, Quiangan, Cayapa and Bintangan, plus the area of the Sierra Madre to the Pacific Ocean in the said trajectory."^[3]

At Balete Pass in Nueva Vizcaya the retreating Japanese under General Tomoyuki Yamashita dug in and held on for three months against the American and Filipino forces who eventually drove them out; the pass is now called Dalton Pass in honor of General Dalton, USA, who was killed in the fighting.