Precision thermal control of large telescope system offers design challenges that require a balance among thermal, mechanical, optical, manufacturing, and systems engineering disciplines. These include optimizing the thermal design around optical sensitivities, choices of thermal control techniques, material selection trades to meet optical metering requirements consistent with other requirements, as well as general configuration trades. This paper presents an overview of the development of the AXAF telescope thermal design, including several major subsystem each with its own unique performance and resulting thermal control requirements. Thermal trades made for the telescope system, HRMS, optical bench, and fiducial transfer system are presented. Results are then applied in a general sense to large high precision optical telescope systems.