Seakeeping analysis is one of classics in marine hydrodynamics. Therefore, there is no need to mention the details in this paper. The main objective of the present study is to develop a program package to predict the linear and nonlinear motion responses and structural loads on marine vehicles, and its extension to various engineering problems. To this end, the computer program called WISH(computer program for linear and nonlinear Wave-Induced loads and Ship motion) has been developed at the first stage, and it has been extended and applied to the seakeeping problems for cruise ships and offshore structures, hydroelasticity analysis such as springing, ship maneuvering, and so on. This paper introduces the theoretical and numerical background of WISH program, some validation results, and application examples.