technology standard allowing electronic musical instruments (electronic instrument) to communicate with one another and with computers (computer).

By the beginning of the 1980s, affordable digital synthesizer keyboards offering a wide range of instrument sounds and effects were widely available. Because the myriad of different computer languages (computer programming language) created by manufacturers to control instruments limited interactivity, an industry working group convened to develop a universal, royalty-free standard. The first synthesizers using MIDI debuted in 1983.

MIDI comprises a set of defined instructions, or MIDI messages, telling a compatible instrument which notes to play, how hard to strike them, with what effects (such as vibrato or sustain), and at what tempo and relative volume. A central MIDI controller, such as a keyboard, can be used to convey musical instructions to one or more MIDI instruments—for instance, an electronic drum machine or a second keyboard. The instruments may also be virtual—software packages residing on a personal computer. Originally, MIDI messages were mainly carried by specialized cables, but in later years protocols such as universal serial bus ( USB), FireWire, and Ethernet became common transports as well.

A live performer may use MIDI to simultaneously control several instruments onstage. In a recording studio a MIDI composition can be edited, resequenced, sped up, slowed down, or adjusted in numerous ways without costly and time-consuming rerecording. This versatility made MIDI composition widespread in popular music, as well as in film and television scores. MIDI message sets have also been written for such wide-ranging purposes as directing stage lighting, controlling amusement park rides, and producing tones for mobile telephones (mobile telephone).