The Gran Telescopio Canarias (GTC) is a 10 m-class telescope which is under construction and will be operational at the Observatorio del Roque de Los Muchachos at the end of 2003. The goal of this paper is to describe the current status of the design and construction of the primary, secondary and tertiary mirrors of the GTC and their opto-mechanical supports. It also summarizes the optical performances expected from the GTC and the error budget of the optical system.