Еhere are several types of disc jockey. Radio DJs or radio personalities introduce and play music that is broadcast on AM, FM, shortwave, digital or internet radio stations. Club DJs select and play music in bars, nightclubs or discothèques, or at parties or raves, or even in stadiums. Mobile DJs travel with portable sound systems and play recorded music at a variety of events. Some mobile DJs also serve as the master of ceremonies (MC) directing the attention of attendees, and maintaining a room-wide focus on what is included in the event's agenda. There are also many competitions that specialise in mixing, scratching or other kinds of techniques.
Other types of DJ use musical performance techniques that allow them to be categorized as performing musicians, depending on the situation. Hip hop DJs not only select and play music using multiple turntables to back up one or more MCs/rappers, but they also perform turntable scratching to create percussive sounds, and are also often songwriters and/or music producers who use turntablism and sampling to create backing instrumentals for new tracks.
In reggae, the DJ (deejay) is a vocalist who raps, "toasts", or chats over p-recorded rhythm tracks while the individual who helps the DJ by selecting tracks to be played is called the selector.
Many electronica artists and producers who also work as DJs often perform music by combining turntablism with keyboards or live electronics. Electronica, hip-hop or reggae DJs also often collaborate and play live music with bands and musicians from several musical genres (rock, heavy metal, jazz or even classical music), using turntables and electronics as musical instruments. According to a 2012 study, there are approximately 1¼ million professional disc jockeys in the world.