Structures for wave attenuation, i.e. floating breakwaters, exist mainly as theoretical concepts. Research into floating breakwaters has a long way to go before a practical floating breakwater is developed. However, the demand for development of such structures has always been strong in the field of offshore engineering. As a result, research and testing of floating breakwaters has been going on actively for a long time (Anchored Buoyant System Committee, 1980) and is continuing even today. The author has been conducting a series of experiments since 1965 with the aim of identifying the future trends of this development activity and designing the possible shapes of floating breakwaters if they are eventually developed for practical applications. The author feels that he has achieved his objectives to a certain extent and has therefore compiled this report as a first step. The primary purpose of this report is to identify an ideal floating body which has the best possibility of commercial development with respect to its shape and wave attenuation characteristics.