Aparri (Ibanag: Ili nat Aparri; Ilocano: Ili ti Aparri; Tagalog: Bayan ng Aparri), officially the Municipality of Aparri, is a municipality in the province of Cagayan, Philippines. According to the 2020 census, it has a population of 68,839 people.

Aparri is a bustling municipality and the primary growth center of Northern Cagayan. It serves as the center of education, commerce and culture in the northern part of the region, which includes towns of the first and second districts of Cagayan, as well as the towns of Apayao and some towns of Ilocos Norte. It serves as the show window of commerce and finance, economic transformation, information technology, livelihood development, fashion and culture, leisure and entertainment, agricultural modernization, and good local governance.

Aparri has an approximate income of ₱250 million. The valley has been one of the largest tobacco-producing sections in the Philippines, and the town has a considerable coastwise trade.

It has a meteorological station located in Barangay Punta where the Cagayan River meets the Babuyan Channel.

The origin of the name Aparri has been disputed. One version says that the town was named by Spanish conquistador Juan Pablo Carreron, who upon landing there in 1581, named the town after the colloquial word for supper in his hometown. Another version claims that the name comes from the Spanish word aparte, or "separate", referring to the town's separation from Camalaniugan and Buguey in 1680. Still another version says that the town's name comes from the Ibanag word apparian, a place where there are many priests.

Aparri was formerly Japanese trading post because of its location at the northern tip of Luzon at the mouth of the Cagayan River. It was the main area for trade for Japan on the island of Luzon. Much of the area was once home to the native Ibanag people, who were at the time in alliance with Japan as an early form of an informal protectorate city-state. It was formally established under Spanish rule in 1605 after the Spanish Crown seized the Philippines and made it part of the Spanish East Indies. The river where Aparri is in was the site of the famed 1582 Cagayan battles, the only major skirmish between Spanish Tercios and Japanese ronin (masterless samurai). Since it was on the route of Spanish Galleons during the great tobacco monopoly in the 16th to the 17th centuries, Aparri was therefore made one of the major Spanish ports of the Galleon Trade on May 11, 1680. The original inhabitants of this town were the Ybanags. Later, as the Spaniards settled and because of its strategic location, Ilocanos and Chinese people settled in the area. In 1771 it was raided by Moro vessels from Jolo. Towards the end of the Spanish occupation and in 1901, at the start of the American occupation, attempts were made to make Aparri the provincial capital of Cagayan, all of which were unsuccessful.

During the Philippine Revolution, Aparri was the site of the landing of soldiers of the Philippine Revolutionary Army led by Daniel Tirona, which marked the beginning of the end of Spanish rule in Cagayan Valley, on 25 August 1898.

In 11 May 1926 Joaquín Loriga and Eduardo Gallarza landed on his first-ever long way in autogyro from Spain to Manila. Before the outbreak of World War II, it became a transshipment point for smuggled goods from China, Taiwan, and other neighboring Southeast Asian nations. Aparri was one of the first places occupied by the Japanese in their invasion of the Philippines during the war, landing there on December 10, 1941. Donald Blackburn's guerrilla forces and the local troops of the Philippine Commonwealth Army and Philippine Constabulary supported the Sixth United States Army Force B, in the capture of Aparri on 20 June 1945.