This project is concerned with the development of ultrasonic techniques for the detection of fatigue and creep damage in materials. This development will allow the detection of damage at earlier stages in power plants and aero engines, resulting in the ability to operate these systems safely for much greater periods. The noncollinear interaction of ultrasound with material nonlinearity will be developed and employed due to its great potential for practical applications. The development and comparison of nonlinear inspection techniques, through modelling and experiment, will provide academic and industrial users with a clear, unambiguous description of the relative performance levels and usefulness of nonlinear ultrasonic inspection techniques, helping future users make the best decisions as to which approach to apply. Finally the testing of this approach on real world samples will confirm its practical applicability. The result will be an understanding of how nonlinear ultrasonic techniques can be used to detect previously undetectable damage in specimens and predict the remaining life in components.