A librettist is someone who produces texts, known as libretti, which are designed to accompany musical performances. The most classic example of a libretto is the text which goes with an opera, but librettist can also write words for musicals, cantatas, oratorios, ballets, and liturgical works like masses and requiems. Being a librettist requires some unique and diverse skills; she or he cannot just have a way with words, but must also have a way with music.
In some cases, the librettist and composer are the same person. However, this is not necessarily always the case. Some very talented composers lacked facility with words, or preferred to focus on the music, allowing someone else to find the words which would fit their compositions. Librettists and composers tend to work closely together during the development of a piece, because the score and words must go harmoniously together or audiences will find the piece jarring to listen to or see.
Sometimes, the words for a piece are written before the score is composed. In other cases, a librettist follows along after a composer, adding words to a musical composition which has already been made. It is also possible for the two to be developed simultaneously, with composer and librettist in close collaboration at every step of the way.
Librettists can work in both verse and plain speech, depending on the needs of the composition. Working with music is challenging because people must think about how the words will sound when sung; something which may sound harmonious when spoken can become disastrous in song, or singers may have difficulty with certain arrangements which push the boundaries of their voices and skills.
Before score or libretto are developed, it is common to sit down and develop a plot. Sometimes the person who does the plotting is not involved in the production of the music or the words, and is simply hired to map out the story. Once the story has been established, people can determine where major musical numbers or arias should occur, and can begin to structure the music and words which will bring the story to life on the stage.
Historically, librettists were sometimes so disregarded that they were not even credited for their work, and the identity behind the authors of the words of some notable musical works is unknown. Today, it is more common to see credit given to the author of the libretto along with other people involved in the creation of the work.