The Secondary Interactions of Surface Waves are treated in two roughly divided case. In Part Ⅰ, the case in which the first order wave has discrete components is discussed, and in Part Ⅱ th case in which it make the continuous spectrum is computed.
　In Part Ⅰ, the main characteristics of the secondary interaction are treated in the one-dimensional problem . They include the case in which the each components of wave have the same direction of progress and the case in which their directions are opposite interaction is obtained, and as an example , the clapotis caused by the oblique incidence of progressive wave on the rigid wall is discussed.
　In Part Ⅱ, we treat the wave which does not contain the progressive components. At first, the case of the one-dimensional wave in the finite depth is treated. Numerical results of the second order nonlinearity obtained by this method are in good agreement with the experimental nonlinear effect. Secondly the problem of the two-dimensional progressive wave in the finite depth is computed. A result of the simple application of this computation shows that, if the first order spectrum of wave profile has the sufficient angular spreading, the second order nonlinear components of frequency spectrum will be nonably different from those without angular spreading.