We present a review of wave packet dynamics in different systems and stress their relation to information on the ultrafast structural changes. We show how dynamical information is obtained from ultrafast optical pump-probe studies on structural changes in isolated molecular systems, before moving to complex systems, such as pure and doped solids, and biological systems. We end with a presentation of new developments in structural dynamics, which are based on the pump-probe scheme, using as probe ultrashort pulses of electron or X-rays. As detection methods, electron or X-ray diffraction or X-ray absorption spectroscopies are discussed.