Breakwaters protecting harbors and coastal areas are key to the economic and social development of many countries, but they are also infrastructures which may result in relevant environmental and social impacts. The construction of new breakwaters in developing countries, together with the dismantling, rehabilitation or repair of old breakwaters in developed countries, should be adapted to the principles of sustainability to produce efficient and resilient systems. Global mean temperatures and sea levels are rising due to climate change, and many environmental variables and numerous ecosystems are evolving. The hypothesis of stationarity, widely assumed in the last century whenestimating the wave climate for the design of maritime structures, is now questionable, and new methodologies are required to design breakwaters in this changing environment. Marine life and ecosystems are affected by construction processes and structures, but the interactions are not well known; marine growth and enhanced biodiversity are usually considered positive environmental impacts of most breakwaters but materials, carbon footprint and energy consumption are negative impacts. The two main challenges in breakwater design are (1) to develop sound design methods valid in a changing wave climate and with rising sea levels, and (2) to adapt design guidelines to build-up, to repair and to dismantle breakwaters in a living environment.
