The finite element method is applied to determine the wave forces and wave fields for various coastal and ocean structures. Wave diffraction and radiation problems are solved by the method. A special infinite element is implemented in a computer program to model an outer infinite sea area. The employed numerical examples are for a vertical breakwater, a gravity-type ocean platform and a floating rectangular caisson. All computed results are compared with ones from experiments and other numerical methods. As a result, it is concluded that the finite element method using infinite elements can give sufficient accuracy to be applicable to most practical structures in the ocean.