The Mid-infrared ELT Imager and Spectrograph (METIS) is one the first three scientific instruments on ESO's Extremely Large Telescope (ELT). At the time of anticipated first light in 2025, METIS will provide diffraction limited imaging, coronagraphy and medium resolution slit spectroscopy in the 3-19 micrometers range, as well as high resolution (R approximately equals to 100, 000) integral field spectroscopy from 2.9-5.3 micrometers. The unique combination of these observing capabilities with an angular resolution of 0.020 sec, and the sensitivity provided by a 40m aperture, make METIS a very powerful tool to study the infrared sky - from objects in our Solar system, the Galactic center, brown dwarfs, evolved stars, and massive stellar clusters to active galactic nuclei (AGN), local starbursts, transient events, and luminous infrared galaxies at intermediate redshifts. Its main scientific focus, however, will be on the study of proto-planetary disks and exoplanets. In this paper, we describe the instrument concept and performance. We discuss the scientific performance of METIS with respect to AKARI, and elaborate on the relevance of the AKARI archive with respect to the METIS observing program.