Many processes induced by the interaction of XUV light with atoms and molecules take place on a very short time scale. The temporal width of the soft X-Ray FEL pulses (100-300 fs) and of the synchronized, tunable optical laser (150 fs) will therefore be ideally suited to gain an insight into the dynamics of these processes. A first series of proposed experiments will serve to characterize the FEL pulses themselves, in particular the intensity, frequency and time structure of the individual pulses by using a cross correlation technique between the XUV photons and a strong infrared pulse. Depending on the final characteristics of the FEL with respect to photon energy range and tunability, these two-photon pump-probe experiments will be extended to further studies, like the investigation of resonances, which are only accessible by a two-photon excitation, the coupling of autoionization states by a strong laser field, which induces drastic changes in the resonance profiles, the wavepacket formation of higher Rydberg states, and the coherent population of excited states by fast dissociation, which will result in the observation of quantum beats on the decay curve of excited fragments.