Norteño is the accordion-and-bajo-sexto border music that emerged along the northern Mexican and US Southwest frontier in the late nineteenth century. The standard four- or five-piece lineup uses a three-row button accordion, the twelve-string bajo sexto for chord work, electric bass, and drums. Songs run in polka 2/4 (the most common), waltz 3/4, or the narrative form of the corrido, at 110–140 BPM. Lyrics run the full range from migration, work, and love to drug trafficking (narcocorrido). What defines norteño, more than any one instrument, is the corrido narrative frame — third-person storytelling reporting real people and real events.

The genre took shape from the late nineteenth century as German, Czech, and Polish immigrants brought the button accordion and polka rhythms to Texas and northern Mexico and locals fused those with existing Mexican song traditions. The 1848 US–Mexico War left the residents of Texas, New Mexico, and California trapped as Mexican-Americans in territory that had suddenly become the United States, and norteño became the sound of a community stripped of its land but not its music. Narciso Martínez (1911–92, Texas-Tamaulipas) codified the button-accordion technique in his 1936 recordings and is remembered as 'the father of norteño.'

The button accordion's characteristic bounce comes from a bi-sonoric mechanism: pressing on the bellows produces one pitch, pulling produces another. That forces the player's fingers into constant back-and-forth motion and gives the phrasing its unmistakable spring. Ramón Ayala's 'Un Puño de Tierra' shows the accordion and bajo sexto unisoning in thirds. In Los Tigres del Norte's vocals, listen for Jorge Hernández's restrained, nasal, narrator's voice — the corrido reciter template.

Los Tigres del Norte, 'Contrabando y Traición' (1974), for the corrido storytelling form perfectly executed. Then 'La Puerta Negra' (1988) for immigrant longing. Ramón Ayala's 'Un Puño de Tierra' for the accordion side. For the romantic strand, Intocable's 'Rincón Abandonado' (1997). Late-night drive music, or Friday-night beer music — norteño was made for the end of a workday.

Bajo sexto ('sixth bass') paradoxically has twelve strings (six paired courses). It descends from an eighteenth-century German luthier's modification. Los Tigres del Norte at their 1968 debut were all in their teens, and the band members were four brothers and one cousin — the same core has held for over fifty years, making them among the longest-running active bands in any genre. The name 'norteño' means 'northerner' in Spanish; on the US side of the border the same music is often called Tex-Mex or Conjunto, with 'Tex-Mex' carrying a Chicano identity and 'norteño' a Mexican one.