Bayombong, officially the Municipality of Bayombong (Gaddang: Ili na Bayombong; Ilocano: Ili ti Bayombong; Tagalog: Bayan ng Bayombong), is a municipality and capital of the province of Nueva Vizcaya, Philippines. According to the 2024 census, it has a population of 72,890 people.

Bayombong is the seat of the provincial capitol and the most populous town of Nueva Vizcaya. The name Bayombong emanated from the Gaddang word “Bayongyong” which means the confluence of two or more rivers. It has been reported that a certain tribe arrived and tried to invade the place, which caused the outbreak of the first tribal war in the area. The site was renamed “Bayumbung” as a sign of the Gaddangs' first victory in fighting for their private domains.

The Gaddang phrase "Bayongyong," which denotes the confluence of two prominent rivers, is where the name Bayombong originated. According to a different interpretation, "bayongyong" refers to a bamboo pole approximately 2 meters long that is used to transport fresh water from wells constructed along riverbanks. When Spanish missionaries spotted the Gaddangs, they were forming long lines and carrying water-filled bamboo poles on their shoulders. When the friars asked about the bamboo water jugs, the carriers answered in unison with "Bayongyong." It was in 1739 when Spanish Augustinian Friars named the place "Bayumbung", which was later changed into Bayombong.

Bayombong is located in the southeastern portion of the current barangays of La Torre North and South, where the Magat River flows. Prior to Spanish colonization, the town was inhabited by the Ifugaos and Gaddangs.

Around 1718 there were tribal clashes between the Ifugaos, the Gaddangs and the Maalats from Isabela, with the Gaddangs gaining the upper hand and displacing the other tribes.

Bayombong was formally founded on April 12, 1739, during the first Catholic mass celebrated in the region, officiated by Father Pedro Freire in a makeshift chapel at the foot of the Bangan Hill. Bayombong came under the administration of Dominican friars as a part of the Paniqui mission a few months after its founding. The pueblo census of 1747 records 470 residents. The names of those considered to be founding fathers of Bayombong were Ramon Cabauatan, Jacinto Gadingan, Vicente Saquing, Ignacio Abuag, Mariano Danao, Domingo Bayaua, a certain Bincatan and a certain Mamuric. All of them were Gaddangs. Their names are remembered today in major streets of the town.

In 1754, the local government was formally organized. A Capitan del Pueblo was appointed as the chief executive. In 1982, the town became the seat of the new Diocese of Bayombong.

From 1773 to 1792, Fray Juan Crespo constructed the brick St. Dominic's church, the convent, and the cemetery next to the church, and started the octagonal tower. By 1829, Fray Juan Molano finished the tower. In 1880 the church building was damaged in an earthquake, while in 1987, a fire destroyed the church and convent. During the 1990 Luzon earthquake, the church belfry collapsed.