The combination of two or more forms of Renewable Energy Sources at the same spatial scale is a highly promising sector, resulting in an increase in the number of installations of hybrid RES systems. In Greece, where abundant resources such as wind and sun are available, the combination of these two renewable forms of energy can contribute to reducing dependence on conventional energy resources, as in hybrid power systems the weakness of a source is offset by the forces of the other. The purpose of this paper is the development of a methodology for selecting suitable sites for the installation of Hybrid Wind and Solar Energy Systems (HWSES) using Geographic Information Systems (GIS). The implementation focuses on the island of Andros, Greece, and the proposed methodology includes the exclusion of areas defined by the Greek legislation and the international experience for both forms of energy. The site selection corresponds to a multi-dimensional process, which includes multiple criteria such as wind speed, solar radiation, distance from settlements, technical infrastructure, environmental and cultural interest and slope. Finally, the areas occupied by wind and solar farms in different licensing stages are excluded from the areas that are available for HWSES siting.