Clear fused silicon dioxide (quartzglass) is one of the simplest but most valuable compounds available to the optical industry. It offers a unique combination of optical, thermal, mechanical, and chemical properties which makes it a very favourable material for a wide variety of space optical applications. Selection of raw material and control of manufacturing processes allow to modify the quartzglass properties within certain limits. The most relevant properties are discussed from a material supplier's point of view, also indicating limitations and constraints, e.g. due to the manufacturing process, and taking into account the typical requirements for space optical material (i.e. functional requirements and specifications for a given application, requirements due to the adverse environment, reliability, and safety requirements). The discussion is based on selected examples of existing space related hardware covering such different fields of applications as transmissive optics (corner cubes for laser ranging, optical windows for space crafts, and space simulation chambers), reflective optics (lightweight mirror blanks, cryogenic mirrors, X-ray telescope), components for micro-gravity experiments (ampoules, calibration standard for mirror furnace).