A bajo sexto (Spanish: "sixth bass") is a musical instrument with 12 strings in 6 double courses, used in Mexican music. It is used primarily in norteño music of northern Mexico and across the border in the music of south Texas known as "Tex-Mex", "conjunto", or "música mexicana-tejana".
The bajo sexto sound provides a strong rhythm in the lower pitched end of a Conjunto band and also provides a strong projection of chord changes across songs.
Northern bajo sexto derives from a similar instrument with five courses, the bajo quinto, developed in central Mexico in the 19th century.
Bajo sextos are traditionally tuned in fourths, what an anglophone guitarist would call All fourths tuning: E,A,D,G,C,F, (from lowest to highest string)
Bajo quintos are tuned the same: A,D,G,C,F (as above)