The purpose of this paper is to describe the Quality System that has been implemented in the Gran Telescopio Canarias (GTC) project to assure the quality of the GTC Telescope. This project is a high-tech scientific-engineering program and therefore it is important, as well as in other programs, that a common working methodology is set up among the participants. The vehicle used to meet this goal has been an Quality System consisting of the Quality Manual and the Operative Procedures. The first step in this effort has been to define what Quality is for the GTC. There are many definitions of Quality, and it was decided to adopt the following definition: `Quality is the fulfillment of the GTC requirements within the Project Schedule and Budget'. The present paper summarizes the process followed to set up the Quality System and the structure of this system, including the Quality Manual and the Operative Procedures.