The dynamics of molecular excitons is essential for the application of organic materials in sustainable technologies like organic electronics or light harvesting. In this thesis, the nature and dynamics of molecular excitons in condensed matter is explored depending on morphology und coupling. To this end, one-dimensional aggregates, amorphous nanoparticles and single crystals are investigated by ultrafast pump-probe spectroscopy. The exciton mobility is extracted from the dynamics and compared to the prediction based on Förster theory. While Frenkel excitons exhibit long lifetimes and high mobility in highly ordered systems, their lifetimes are significantly reduced in systems with low order due to relaxation into other excitonic states. The order furthermore increases the mobility, preserves the delocalization and allows for exploitation of the splitting of the excited state. In order to avoid the usage of improper approximations, the coupling is determined based on the model proposed by F.C. Spano and co-workers. The procedure is modified in order to account for deviations from the theory in practice. Both approaches, namely analyzing the dynamics and applying Förster theory, yield consistent results. Thereby the contribution of the coupling and the spectral overlap to the mobility are determined separately for all systems. With this approach the observed differences in the exciton mobility are explained quantitatively.