This study presents a novel method for the selection of sites for floating wind farms based on marine spatial optimization. After providing a review of the present state of the art, a tool based on geographic information systems is presented, consisting of three main stages and built in Python language. The first stage collects and analyses the information of the different regulatory bodies, marine spatial planning, maritime concessions and other sources. The second stage excludes not feasible sites for floating wind farms, based mostly on marine space use and on environmental constraints. The third stage characterises the available locations based on five major categories that are spatially dependent: metocean data, viability data, logistics, facilities, marine environment and techno-economic data. The proposed methodology is implemented at the Europe Atlantic coast, with specific reference to Portugal, Spain and France. These three countries together combine 3.362.408 km2 of the Atlantic Exclusive Economic Zone, where in only 0.22% of that area could host floating offshore wind turbines. While further detailed studies about locations and legislative considerations are required, the effort made has contributed to eliminate unsuitable areas and identify those where sustainability can be maximized.