A method for assembling a floating offshore wind farm, for an assembly in a body of water of at least N floating offshore wind power plants, N being an integer greater than or equal to 3, wherein each floating offshore wind power plant comprises at least one wind turbine mounted on a floating structure, said wind turbine comprising an assembly of several constituent elements (4, 40; 5; 6) including at least one mast fixed on the floating structure and composed of a stack of several mast sections, a turbine fixed on a top of the mast, and blades coupled to said turbine, said method for assembling a floating offshore wind farm comprising the following steps of: - providing and placing at least N floating structures on the body of water; - providing a plurality of mast sections for assembling at least N masts; - providing turbines and blades for at least N wind turbines; said method for assembling a floating offshore wind farm being characterized in that it comprises the following steps of: - selecting, among the at least N floating structures, at least one floating structure called floating mounting structure, the other floating structures being called receiving floating structures; - fastening a lifting device (7; 700) on the floating mounting structure; - moving the floating mounting structure up to one of the receiving floating structures, and using the lifting device (7; 700) to lift and mount at least one of the constituent elements (4, 40; 5; 6) of the wind turbine onto said receiving floating structure; - repeating the preceding step for the other receiving floating structures. said method for assembling a floating offshore wind farm comprising the following steps of: - providing and placing at least N floating structures on the body of water; - providing a plurality of mast sections for assembling at least N masts; - providing turbines and blades for at least N wind turbines; - providing and placing at least N floating structures on the body of water; - providing a plurality of mast sections for assembling at least N masts; - providing turbines and blades for at least N wind turbines; said method for assembling a floating offshore wind farm being characterized in that it comprises the following steps of: - selecting, among the at least N floating structures, at least one floating structure called floating mounting structure, the other floating structures being called receiving floating structures; - fastening a lifting device (7; 700) on the floating mounting structure; - moving the floating mounting structure up to one of the receiving floating structures, and using the lifting device (7; 700) to lift and mount at least one of the constituent elements (4, 40; 5; 6) of the wind turbine onto said receiving floating structure; - repeating the preceding step for the other receiving floating structures. - selecting, among the at least N floating structures, at least one floating structure called floating mounting structure, the other floating structures being called receiving floating structures; - fastening a lifting device (7; 700) on the floating mounting structure; - moving the floating mounting structure up to one of the receiving floating structures, and using the lifting device (7; 700) to lift and mount at least one of the constituent elements (4, 40; 5; 6) of the wind turbine onto said receiving floating structure; - repeating the preceding step for the other receiving floating structures.