This paper describes an investigation into using incompressible smoothed particle hydrodynamics (ISPH) to simulate the overtopping of a coastal structure such as a breakwater. The paper presents the ISPH formulation that employs the multiple boundary tangent method and the latest developments such as particle shifting that produce noise-free pressure fields. The numerical model is compared with experimental overtopping data for a solitary wave and a crest-focussed wave group approaching a trapezoidal breakwater. The ISPH model is shown to produce close agreement for the free-surface evolution for both types of wave and generates overtopping volumes in satisfactory agreement with experimental data. Closer agreement with experimental data is obtained for ISPH compared to more popular weakly compressible SPH for the same resolution or particle size. Future work identifies conducting a convergence study and using more sophisticated boundary treatments.