MATISSE (the Multi AperTure mid-Infrared SpectroScopic Experiment) is foreseen as a mid-infrared spectro-interferometer combining the beams of up to 4 UTs/ATs of the Very Large Telescope Interferometer (VLTI). MATISSE will measure closure phase relations and thus offer an efficient capability for image reconstruction. In addition to the N band, MATISSE will open 2 new observing windows at the VLTI : the L and M bands, which all belong to the mid-infrared domain. Furthermore, the instrument will offer the possibility to perform simultaneous observations in separate bands. MATISSE will also provide several spectroscopic modes. In summary, MATISSE can be seen as a successor of MIDI by providing imaging capabilities in the entire mid-infrared accessible from the ground. The extension of MATISSE down to 2.7 micron as well as its generalisation of the use of closure phases make it also a successor of AMBER.
MATISSE will exploit the astrophysical potential of the VLTI by overcoming the ambiguities often existing in the interpretation of visibility measurements. The unique performance of MATISSE is partly related to the existence of the four large apertures of the VLT (UTs) that permits to push the sensitivity limits to values required by selected astrophysical programs such as the study of Active Galactic Nuclei and protoplanetary discs. Moreover, the evaluated performance of MATISSE is linked to the availability of ATs which are relocatable in position in about 30 different stations allowing the exploration of the Fourier plane with up to 200 meters baseline length. Key science programs using the ATs cover for example the formation and evolution of planetary systems, the birth of massive stars as well as the observation of the high-contrast environment of hot and evolved stars.