There are many kinds of musicians, but some of the largest categories are these: instrumentalists (those who play instruments), singers, conductors, composers, songwriters, arrangers, orchestrators, copyists, and teachers.

The Department of Labor reports that there were 187,600 musicians and singers employed in the United States in 2018. Musicians, or instrumentalists, play many kinds of instruments, but those instruments usually fall into specific categories. String instruments produce sound when their strings are either plucked or strummed, as is the case with the guitar and the mandolin, or bowed, as is the case with the cello, the viola, and the violin. Wind instruments, or woodwinds, produce sound when air is blown through them, as do brass instruments, which are sometimes called brasswinds. Some woodwinds have mouthpieces equipped with reeds. When the player blows through the mouthpiece, the reed vibrates, producing sound. Instruments such as clarinets and saxophones use a single reed, whereas instruments such as oboes and bassoons are equipped with double reeds. The flute, however, does not use reeds at all. Instead, it produces sound when a player blows air at an angle against a fixed mouthpiece. Brass instruments also generally have a fixed mouthpiece. Percussion instruments, such as drums, produce sound when they are struck by a hand or by an object such as a stick or a mallet. The piano, which produces sound when its strings are struck by hammers that are activated when a pianist presses the piano's keys, is also considered a percussion instrument.

Singers use their voices to make music. In most cases, singers sing words, or lyrics, that are intended to match the music accompanying them. In some cases, however, singers use their voices as instruments. In Western classical music, singing without words is called vocalization. In jazz, some singers use a technique called scat singing, which involves using sounds in place of words.

Conductors "play" an orchestra, choir, or other ensemble rather than an instrument. It is the job of the conductor to ensure, among other things, that the musicians play the correct notes at the correct times, that instruments or voices start and stop at the right times, that instruments and voices are neither too loud nor too soft and are in balance with one another, that the music being performed is interpreted in an appropriate manner (which usually means honoring the composer's intentions), and that the music has an impact—usually an emotional impact—on the listeners. Conductors must know the music they are conducting inside and out, which means that much time must be spent in preparation before the conductor works with the ensemble. Conductors use their hands or a baton to indicate the basic rhythm that is being played by the ensemble, which helps the musicians to keep together. Conducting is a demanding profession that requires a very high level of knowledge, expertise, sensitivity, and intuition. According to the Department of Labor, about 64,700 music conductors and directors worked in the U.S. in 2018.

A musical composer is a person who creates original music. Some composers, such as those who write orchestral music, write their music using notation, which ensures that their music can be played by musicians who can read that notation. In the case of classical music, the written music that results is very detailed. Some recording artists who are composers create music by giving oral or other nonwritten instructions to their musicians, using no notation whatsoever, yet the pieces they create are considered compositions. Many songwriters (composers who specialize in the song form) who record their songs give their musicians a lead sheet that consists of a melody and a set of chord changes, which gives the musicians basic instructions yet also allows them the freedom to interpret the music in specific ways of their own choosing. In many cases, composers or songwriters who do not read music and cannot write notation hire formally trained musicians to write down their songs, so that the written music can be used by others. Songwriters may write both music and lyrics or may write one or the other exclusively. Those who do not write lyrics work with a lyricist, who provides the words.

Arrangers generally create a musical background for a preexisting melody. An arranger may create an introduction and a coda (ending) for a melody as well as add countermelodies (additional melodies) to the original melody. In effect, the arranger composes additional material that was not provided by the original composer and ensures that the original melody is set off by its background in an effective manner. An orchestrator takes a piece of music, perhaps one that already has a basic arrangement, and assigns the parts to specific instruments in the orchestra or other ensemble. For this reason, the orchestrator must have a tremendous amount of knowledge regarding exactly what the various instruments can and cannot do. An orchestrator may decide, for example, that a particular melody should be played by a solo flute or by a flute and an oboe, so that a very specific sound will be achieved. An orchestrator must also know how to notate parts for various instruments. All the choices that the orchestrator makes will have a significant impact on the way the music will sound. Arranging and orchestrating are very closely related, and many professionals perform both tasks. Many composers also do their own arranging and orchestrating.

Copyists take the rough drafts of written music provided by composers, arrangers, or orchestrators and turn them into polished final products. Good copyists know how to determine the best way to write various passages of music in order to make them easily playable. As any musician who has tried to read a poorly written piece of music knows, the job of the copyist is critical. A performance may be ruined by badly written music, especially when the musicians are playing music that they have not had a chance to rehearse sufficiently, which is often the case. A copyist may have to rewrite parts that have not been written correctly. If a composer has written a piece of music intended for harp as if it had been intended for piano, for example, the copyist will recast the music in the specific notation that harpists use. Many copyists work on computers, but some copyists still work by hand. The copying required for a large orchestral work typically costs thousands of dollars.

Many musicians are teachers. Some teach full time in institutions such as colleges, conservatories, high schools, and grade schools, while many others teach privately or run their own small teaching studios. Many teachers teach because they love teaching; for others, however, teaching supplements their meager performance income and enables them to survive. There were 94,310 postsecondary music teachers employed in the U.S. in 2018, according to the Department of Labor.

There are many types of music that musicians play, such as classical music, blues, jazz, world music, rock, pop, country music, and folk music. Some musicians play only one kind of music, while others play in a wide range of styles on various occasions. Some musicians spend most of their time playing concerts or club dates, while others, called studio musicians, play mostly for recordings.

Classical musicians may play in an orchestra or sing in a choir, perform chamber music (music for small groups such as string quartets and small vocal ensembles), act as featured soloists who travel from town to town playing with various orchestras, or work as studio musicians, providing recorded music for films, television, radio, compact discs, and so forth. Classical musicians must be highly trained. They generally begin studying music privately when they are very young. Later, they study in conservatories, and many of them obtain advanced degrees. Playing in orchestras and other ensembles is an essential part of their training.

Like classical musicians, good jazz musicians are highly trained, but their training is not necessarily as formal as that of classical musicians. Some jazz musicians study in conservatories and have advanced degrees, but many learn their trade by studying on their own, studying privately with other jazz musicians, and by honing their skills in various groups. The study of improvisation, the art of creating music on the spot, which is the jazz player's stock in trade, requires a tremendous amount of harmonic knowledge as well as technical facility, intuition, good taste, and knowledge of the jazz tradition. Jazz musicians play concerts, festivals, club dates, and studio dates. In addition, many jazz musicians spend part of their time playing other kinds of music.

Blues, folk, rock, pop, world music, and country music performers tend to be, but are not always, self-taught. Instead of studying music formally, they learn by playing in bands, picking up information from other musicians, and studying privately. Many of these players do not read music. Yet more and more young players in these categories are choosing to attend schools of music, hoping to increase their marketability by increasing their skills, which is a wise move for most players.

Generally speaking, blues, folk, rock, pop, world music, and country performers make money by playing in clubs, at concerts, at festivals, and by doing studio work. They also make and sell recordings, which is a major source of income. Some artists are primarily recording artists—in fact, some do not perform live at all—whereas others make most of their living by performing. The most popular of these performers also make music videos, which serve to publicize the musicians and