The plena is an important genre of folk music in Puerto Rico and typically associated with coastal regions of the island. Like the corrido in Mexico, the plena is a narrative song that details the pains and ironies of people and life in their communities.

An excellent modern example of this genre is the song El Bombón de Elena recorded by Ismael Rivera and Rafael Cortijo.

Origins of the plena
There are several theories on how and when the plena originated. The most popular theory on the origins of the plena is that it originated in the city of Ponce, on the southern coast of Puerto Rico, around 1920, as this popular plena, San Anton would suggest. However, it is more likely that it was much earlier, with examples from Puerto Rico and elsewhere dating back several decades. Music historian Francisco Lopez Cruz makes a distinction between the music and dance components of the plena, claiming that the musical elements can be traced back to songs as around 1875, preceeding the dance elements which can accurately be said to have its roots in Ponce.

In any case, it is clear that this musical genre has roots in African music and dance. The plena became popular in the early part of the 20th century in the sugar-growing areas along the southern coast of the island. It provided the slave population and the peasantry, with a musical expression of their life. Similar music genres, according to Lopez Cruz, are the "corrido" of Mexico, the "romance" of Spain, the calypso of Trinidad, the "porro" of Colombia and the merengue of the Dominican Republic. This is not to say that the plena comes from or is based on those other genres, but simply that they all share some characteristics. Interestingly, the experts make no mention of "jíbaro" or Taíno influences, as as is sometimes assumed.

As the rural workers moved to San Juan and other urban areas in the recent past, the plena became a part of the urban cultural life, and, as is typical of folkloric music everywhere, was performed for entertainment at informal social gatherings. The music evolved as musicians added instruments like horns to its complicated rhythms and the typical "soneos", the improvised call-and-response vocals also found in other genres, including bomba and salsa.

The lyrics
The plena's words deal with contemporary events and is often called "el periodico cantado", or a kind of living newspaper. Singers recite the events of the day and often satirize local politicians or scandals. Sometimes plenas are filled with biting satire; at other times, they comment on major news events of the day, such as a devastating hurricane. But not all plenas are historically significant or deal with social commentary. Some are just fun, or personal, playful or humorous, with no relationship to news, events, politics, or protest. But whether the lyrics deliver a serious protest or lighthearted fun, the plena remains a vital cultural part of the community's expression.

Vocalists in a plena would include a soloist and chorus singing in a call and response, antiphonal pattern. The chorus consists of no more than two singers, one of which might sing harmony an octave higher; called "requintar".

The choreography
The plena may be danced, but that is less important than the lyrics and melody, in contrast to the bomba. The choreography is quite simple with pairs dancing together although originally evidence indicates that they danced apart. While bomba is not usually performed without the dancers, the plena can be. The plena drummers do not necessary dialogue with the dancers as is done in a bomba, but they do perform solos. Some modern plenas are played at a blistering pace, inspired by the reggae genre.

The instruments
Plena music is played in 2/4 time, with instruments that typically would include several sizes and pitches of panderetas, also called "panderos". The panderetas are the most characteristic instruments of the plena. A pandero is a hand held drum similar to a tambourine but without the cymbals, with an animal skin stretched over a frame. Three panderetas of different sizes are needed for a complete plena ensemble.

Two supporting drums are also typical of the plena instrumentation. One is called a seguidora, which provides the rhythmic foundation, and the second is the lead drum, called a requinto which reinforces and accents portions of the rhythmic structure of the song text and is also used for improvisatory solos. Another important instrument used in a plena would be a güiro, whose primary role is to play a fixed rhythm but which may also be used to play solos. Other instruments might include a cuatro or guitar and conga drum, and perhaps a single maraca. An accordion or harmonica may also be used, but these are not typical. Some plena ensembles include a trumpet, clarinet, or some other wind instrument.

The link to bomba
Many people link the bomba and plena genres together, based on historical and musical reasons. Both bomba and plena share many musical characteristics and are both clearly derived from West African musical traditions. Both use two or three drums of different sizes and pitches playing inter-related rhythms. Both also use a solo singer together with a chorus and the lyrics of both relate to the everyday life of people in the community. In fact, the two names, "bomba y plena," are often elided in speech, resulting in a single term: "bombayplena" that is well understood in Puerto Rico. But despite these common aspects between the two genres, there are also distinct differences. They differ in their instrumentation by way of the types of drums they use. They differ also in the nature and importance of the dance, as well as the verse structure and its content.

The composers
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 A Jiménez, known as 'El Canario'. Certainly, there were many others, including such greats as Ismael Rivera and Rafael Cortijo.

The revitalization of plena today
By the later part of this century, the plena had ceased to be the pre-eminent genre of popular music for the common folk. It was surpassed in the commercial market by salsa, merengue and more modern musical genres. Even imported genres like rock music, did more to satisfy the desires of the younger generation that drove the music industry, than the old folk music genres. However, in recent years the plena has been revitalized with new sounds by modern artists in Puerto Rico and New York. In the 1960's and 1970's, artists such as César Concepción, Mon Rivera, updated and modernized the plena with big-band style instrumentation: trombones, congas, and 'sonero' type vocal arrangements. This brought on a plena revival that has blossomed in the 1990's, with new stars such as Plena Libre.

Even salsa artists have played a part in the revitalization of the plena. Popular salsa pioneer, Willie Colón, made a series of influential albums in the 1970's that not only reinterpreted traditional plena in a salsa music format, but featured well-known traditional plena artists. Two recordings paired Colón with Yomo Toro, the well known cuatro master of Puerto Rico. These recordings included a variety of plena and jíbaro music played in the style of New York salsa. Simlilarly, Colón turned to his roots and made two albums with Mon Rivera in 1975-76 , featuring plenas and bombas in salsa style. The significance of these four albums was telling and timely. They validated the plena as a traditional music genre, for the younger generations of Puerto Ricans who were only familiar with salsa and thought that the old folk music was passé.