This paper discusses some of the ways in which techniques dealing with potential flow theory are now being used to predict wave loads on offshore structures and their response to that loading. Following a discussion of underlying assumptions, the basic theory is developed, and then results presented for one particular application, that of wave energy devices. Numerical result from one particular computer program, NMIWAVE, are compared with both experimental measurements and exact analytic solutions in order to validate both the basic mathematica1 assumptions and the computer model.