The best cuatros are still crafted in much the same manner as they were hundreds of years ago.
Not that anyone calls it that, but most modern cuatros have five strings, or actually, 10 strings, five sets of two with each pair tuned to the same note.
The cuatro and the Caribbean island's folk-loric music are so intertwined they are all but one and the same.
It matters little that the shape has changed over the centuries or that the cuatro may now have as many as ten strings.
While Puerto Ricans defend the cuatro as exclusively their own, Venezuela claims its particular version, as well as a strikingly similar instrument called the tiple.
The cuatro is my blood," says Puerto Rico's internationally known guitarist, Yomo Toro.
When Toro started using the cuatro in tropical music groups, he surprised a lot of traditionalists, but he proved that the instrument adapts easily to many styles.
Where Yomo Toro has found popularity adapting the traditional cuatro style to the world of tropical music, others have expanded the instrument's potential into very nontraditional styles.
Taking perhaps even more liberties, a Puerto Rican group called "Jibaro Jazz" has proven the cuatro is as adept at pure improvisation as is the most modern electric guitar.
Across the Caribbean, Venezuelan Mauricio Reyna has devoted himself to broadening the base of interest in his country's version of the instrument, the cuatro Venezolano.