A mainstay of Puerto Rican traditional music and a national cultural emblem or icon which resembles a cross between a small guitar and a violin. It is the most familiar of the three instruments which make up the Puerto Rican orquesta jibara - the others being the tiple and the bordonua. This is an instrument of the jibaro, rural farmers, and also the name of the music they played on cuatros and guitars and guiros. It is also used to accompany aguinaldos, the Puerto Rican Christmas songs, performed by musicians travelling from house to house.

The instrument is roughly violin shaped, although the the bridge is typical of most guitars. The Puerto Rican cuatro has 10 steel strings in 5 courses, tuned in fourths from low to high, with B and E in octaves and A, D and G in unisons. It is played with a flat pick and sounds like a cross between a 12-string guitar and a mandolin.

There is also a Venezuelan cuatro which is quite different. It has 4 single nylon strings, tuned (A4,D5,F#5,B4) or (A3,D4,F#4,B3). It is similar in shape and tuning to the ukulele, but their character and playing technique are vastly different. It is tuned in a similar fashion to the traditional D tuning of the ukulele, but the B is an octave lower. Consequently, the same fingering can be used to shape the chords, but it produces a different transposition of each chord. This instrument is also known as the guitarra pequeña, guitarrita, or guitarilla, and also exists in a 5-string version (cinco), and a 6-string version (seis). Variants include the bandola.