The theory of the diffraction of water-waves has previously been limited to twosimple cases; the diffraction around a semi-finite breakwater and the diffractionthrough an opening in a rigid plane. Another useful practical configuration consideredhere is two breakwaters at an angle, with a gap at the corner in one ofthe breakwaters. The parameters are the angle, the breadth of the gap and theangle of incidence of the wave train. The waves are assumed to be of small amplitude.Numerical results agree well with the classical solution for the case wherethe two breakwaters lie in the same plane. Experiments with two sets of parametershave been made in a tank and have also shown good agreement with the theory.