In this paper the adjoint to the full WAM model, a third-generation ocean wave model, is presented. This adjoint, ADWAM, was constructed from the WAM source code level by using an automatic adjoint code generator. As a first application, ADWAM has been used for inverse modeling with the object to get a better insight into the numerical values of several model parameters in the WAM source terms. Two adjoint runs were performed. For the first, both deep water fetch data, which were compiled by Kahma and Calkoen, and shallow water fetch data, which were obtained from Lake George by Young and Verhagen, were considered simultaneously. The second adjoint run was performed for a storm which occurred in the North Sea in February 1993. Both adjoint runs lead to a consistent trend: a reduction in the integral strengths of both the wind input and the whitecapping source terms with respect to the best estimate so far. In this best estimate, the whitecapping dissipation is proportional to the square of the wave steepness. Both runs in addition suggested that this dependency should be increased to a cubic one. It was found that the improved model performance was not only limited to the optimization windows but consistent for other intervals that were not optimized. ¿ 1998 American Geophysical Union