Plena is a traditional form of Puerto Rican music. It is a blend of Spanish, African, and possibly native Taino music. The music is related to similar music in Trinidad and Barbados.

The music's beat and rhythm are mainly due to drums derived from those African drums common to Northern and Central Africa, more specifically called panderetas or panderos. Other instruments heard in plena music are the cuatro, the guiro, the maracas, and a requinto.

The rhythm itself was reportedly created by a black couple who were originally from Barbados and who lived in the Joya del Castillo section of Ponce, Puerto Rico, probably occurring as early as 1919. There is some speculation that "plena" is a corruption of "Play, Anna", the alleged initial call used by the husband to ask his wife to assist him in his drumming by playing the counterpoint that characterizes plena. However, Puerto Rican historians such as Ricardo Alegria have debased this as an urban legend, since the name plena had been used to depict the danceable part of traditional merengue as early as the 1850's.

Plena quickly became a "singing news paper" for the lower classes, and used to spread messages among people, similar to the corridos in Mexico. The traditional epicenter of plena was probably San Anton, a barrio of Ponce.

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. This is an African characteristic. The lyrics of the songs deal with current events. The singer will recite the events of the day and usually criticizing the local politicians, or will discuss the daily scandals, or horrific events such as hurricanes and its devastation. (From Wikipedia)

In the 1920's or earlier this music was recognized. Traditionally was associated with the region around the city of Ponce in the southwestern portion of the island. Group of singers who used large Spanish tambourines (panders) made a rhythmic beat of one and three. It is organized into a pattern which suggests that it has grown in relationship with the 'Merengue' of Haiti and Dominican Republic. Today the rhythm has been adapted to the music of the bands which play in the larger cities of Puerto Rico and its compositions are arranged in a style to that for other Afro Caribbean music. It details the pains and suffering of people and their life in their communities. This music unlike the 'bomba' it blends wide cultural background from Puerto Rico while the 'bomba' is only African roots.