The Mid-infrared ELT Imager and Spectrograph (METIS) will provide the Extremely Large Telescope (ELT) with a unique window to the thermal- and mid-infrared (3–13 µm). Its single-conjugate adaptive optics (SCAO) system will enable high contrast imaging and integral field unit (IFU) spectroscopy (R ~ 100 000) at the diffraction limit of the ELT. This article describes the science drivers, conceptual design, observing modes, and expected performance of METIS.