WindFloat is a floating foundation for very large offshore wind turbines. This paper describes the hydrodynamic analysis of the hull, as well as ongoing work consisting of coupling hull hydrodynamics with wind-turbine aerodynamic forces. Three main approaches are presented in this paper: - The numerical hydrodynamic model of the platform and its mooring system; - Wave tank testing of a scale model of the platform with simplified aerodynamic simulation of the wind turbine; - FAST, an aerodynamic software package for wind turbine analysis with the ability to be coupled to the hydrodynamic model. These conference proceedings include two other papers presenting the design basis and main systems of this floating foundation [1], as well as structural analysis of the hull and mast [2].