The growing global demand for renewable energy is accelerating the development of offshore wind technology, with floating offshore wind turbines (FOWTs) emerging as a key option to harness wind resources in deeper waters. This technology has great potential but is still at an early stage, where high costs, technical complexity, and design uncertainties remain major barriers to large-scale deployment. To make FOWTs a feasible option, optimization is essential to reduce costs and improve performance, while a multidisciplinary approach is required to properly account for the coupled nature and complexity of the system. Within the INF4INiTY project, this thesis develops a multi-objective optimization methodology for the GICON-SOF Tension-Leg Platform supporting the IEA 15-MW reference wind turbine.