MIDI controller keyboards are electronic keyboards, designed to trigger sounds in synthesizers and sound modules, as well as to enter notes into MIDI sequencers. There's a microswitch under each key connected to a MIDI processor. It will sense what keys are pressed, how long they are held, and sends this data to other devices. Velocity sensitive keyboards will also sense how hard the keys are pressed, to add dynamics to the note data. Some keyboards have an extra sensor for aftertouch, for added expression. When the key is held down, you can apply more pressure to trigger the aftertouch sensor. This aftertouch data can be used to alter the sound (i.e. add vibrato). Most controller keyboards are also equipped with pitch and modwheel and various other knobs, sliders and buttons to send MIDI data, such as program change, and other assignable control messages to the receiving MIDI devices. MIDI controller keyboard usuall don't come with built in sounds, (if the do, they are called synthesizers).

A MIDI keyboard is a piano-style digital keyboard device used for sending MIDI signals or commands to other devices connected to the same interface as the keyboard. MIDI is an acronym for Musical Instrument Digital Interface (protocol). The basic MIDI keyboard does not produce sound.