The optical design of METIS including a Warm Calibration Unit (WCU) outside and the Common Fore Optics (CFO), the Single-Conjugate Adaptive optics system (SCA), the L/M band high resolution spectrograph (LMS) and the imagers and spectrographs (IMG) in the L/M and N/Q bands, all inside the cryostat (CRY). The Laser Tomography AO (LTA) unit is part of a design study and may not be realised.