A multi - cylinder TLP design concept of a floating structure is presented for supporting a 10 MW Wind Turbine (WT). The present design represents the development of a floating structure for offshore wind energy sources exploitation. Focusing on the conceptual design of the proposed TLP floating structure for the 10MW wind turbine, the combined effect of water waves and wind on the floating offshore wind turbine is studied. A design - oriented solution method for the coupled dynamics of the floating structure in the frequency domain is presented. By properly accounting for the aerodynamic characteristics of the WT through a reduced order model that projects the WT aerodynamics onto the six degrees of the floater’s motions. They are combined with the hydrodynamics of the floater and the tethers stiffness to set up the coupled dynamic equations in the frequency domain. The calculations where obtained using in-house developed computer codes. The hydrodynamic characteristics of the floating arrangement of the 10MW WT, the mean annual wind power density and wave energy flux, as well as the univariate design values of wind speed and sea-state intensity near to Kasos Island (35.34° Ν, 26.80° Ε) at the Aegean Sea are also presented.