The purpose of the Gran Telescopio de CANARIAS (GTC) project is the design, construction, erection and startup of a telescope with a segmented primary mirror equivalent to a circular aperture of 10 m in diameter. The GTC project was created to satisfy the needs of Spanish astronomers for more telescope time and larger telescopes. The GTC project does more than simply increment the list of `8-10 meter class' telescopes. Its requirement for higher specifications differentiates it from other telescopes of its generation. The GTC will combine a large collecting surface with excellent image quality and suitably optimized observation in both the visible and the infrared. The Gran Telescopio de CANARIAS Project Office Telescope Group, based in the Canary Islands, together with a joint venture of Spanish companies, are developing the telescope mechanics systems, taking into account the scientific requirements established. This paper summarizes the scientific requirements that have technically led the design process of the telescope mechanics and the features that have been incorporated to meet said requirements.