Plymouth Breakwater is a 1,560-metre (1,710 yd) stone breakwater protecting Plymouth Sound and the anchorages near Plymouth, Devon, England. It is 13 metres (43 ft) wide at the top and the base is 65 metres (213 ft). It lies in about 10 metres (33 ft) of water. Around 4 million tons of rock were used in its construction in 1812 at the then-colossal cost of £1.5 million.

Plymouth Sound, or locally just The Sound, is a deep inlet or sound in the English Channel near Plymouth in England.