Plena is a folkloric genre native of Puerto Rico. Its creation was influenced by African and Spanish music.

The music's beat and rhythm are usually played using hand drums called panderettas or panderos or pleneras and are accompanied by a scrape gourd, guiro. Pleneras resemble tambourines but without the cymbals. These are handheld drums with stretched animal skins, usually goat skin, covering a round wooden frame. They are three different-sized panderettas used in plena: the Seguidor (the largest of the three), the Segundo (the medium-sized drum), sometimes called Banao or Punteador, and the Requinto (the smallest one). There is a disagreement on whether the panderetas typically used in Puerto Rico today are adapted from instruments known in Spain from the time of the Moors known as an "adufe", or from similar African instruments. An advantage of this percussion arrangement is its portability, contributing to the plena's spontaineous appearance at any social gathering. Other instruments commonly heard in plena music are the cuatro, the maracas, and accordions.

The fundamental melody of the plena, as in all regional Puerto Rican music, has a decided Spanish strain; it is marked in the resemblance between the plena Santa María and a song composed in the Middle Ages by Alfonso the Wise, King of Spain. The lyrics of plena songs are usually octosyllabic and assonant. Following the universal custom the theme touches upon all phases of life-romance, politics, and current events—in fact, anything which appeals to the imagination of the people, such as the arrival of a personage, a crime, a bank moratorium, or a hurricane.

Plena was often called the periodico cantado or "sung newspaper" for the lower classes because it spread messages among people, similar to the corridos in Mexico. The traditional center of plena was probably San Antón, a barrio of Ponce, although the black neighborhood of Loíza is also mentioned as the heartland for the genre. Its popularity peaked in the 1920s.

Plena is played throughout Puerto Rico especially during special occasions such as the Christmas season, and as the musical backdrop for civic protests, due to its traditional use as a vehicle for social commentary. Whenever plena is played the audience also joins in the singing, clapping, and dancing.

As a folk genre, there have been many good composers, some well known in their day and into the present. Perhaps one of the genre's most celebrated composers and performers was Manuel Jiménez, known as 'El Canario'. Certainly, there were many others, including such greats as Ismael Rivera, Mon Rivera (the Younger), and Rafael Cortijo. The genre has had a revival recently, as evident by the emergence of many plena bands (such as Plena Libre) and its use in various songs, such as Ricky Martin's recent song "Pégate".