The GEMINI telescopes project in an international partnership between the United States of America, the United Kingdom, Canada, Chile, Brazil and Argentina to built two eight-meter astronomical telescopes, one on Mauna Kea, Hawaii and one on Cerro Pachon, Chile. The top science requirement of these instruments is superb image quality. It is intended that, in the absence of atmospheric seeing, the telescopes would deliver fully diffraction limited long exposure images in the K-band (2.2 μm). Accordingly, the telescopes and their enclosures have been designed and are being constructed with exacting attention to optical quality, thermal equilibrium and servo control accuracy. This, and the excellent natural seeing at the sites - FWHM = 0.45 arcsec (median), 0.25 arcsec (best 10th percentile) - will make the GEMINI telescopes performances well suited for further improvement by adaptive optics (AO). The Mauna Kea telescope will be highly optimized for performance in the thermal infrared, with an emissivity specification of <4% (2% goal).