Our understanding of the elementary processes of charge and energy transfer in molecular systems has developed at an enormous pace during the last years. Time-resolved spectroscopy has opened a real-time look at the microscopic details of molecular dynamics not only in the gas, but also the condensed phase. Atomic scale structures are available for a virtually uncountable number of biological systems which in turn triggers spectroscopic investigations like in the case of photosynthetic complexes or photoactive proteins. The emerging combination of structural and temporal resolution in time-resolved X-ray crystallography bears an unprecedented potential for the understanding of the interrelation between molecular structure and function. On the theoretical side, accurate electronic structure methods are becoming available for systems with hundreds of atoms, thus providing valuable information about interaction potentials governing molecular motions. The combination of quantum and molecular mechanics offers a way to condensed phase systems. Quantum dynamics methods, on the other hand, suffer from exponential scaling. Fortunately, the detailed information contained in the full wave function is quite often not needed and effective model simulations based on quantum chemical, classical molecular dynamical, but also experimental input are appropriate...