MIDI: Obtaining and analysing interferometric data in the mid-infrared

MIDI, and the VLTI in general, is offered as an interferometric system to a wide community of astronomers who do not necessarily have a deep knowledge on how an interferometer works. This text intends to provide the first basics of the MIDI interferometer. It provides a short description of its instrumental layout and a bit of history, followed by an introduction of the data reduction with two software programs: MIA and EWS.