An oscillating water column type wave energy power plant has been set up off the south-west coast of India near Trivandrum. The system consists of a caisson 23.2 m x 17 m in plan, 18.3 m high in reinforced concrete, resting on a prepared sea bed in 10.2 m water depth. The caisson was built and placed in position in December 1.990 and the power module erected in October 1991 and trial runs on power generation started in November 1991. The paper explains the concept of the caisson and describes its analysis, design, construction and installation aspects. The caissons can simultaneously be used as a breakwater for a harbour.