The big bang and its immediate aftermath remain one of the great mysteries in science, and it is likely that only an inter-disciplinary approach using both fundamental particle physics and cosmology will get us closer to understanding the origin of our universe. Currently the most promising framework for a theory of all particles and forces is string theory; however, it has been notoriously difficult to address cosmological issues within the theory. Only in the last few years has it been possible to construct stringy inflationary models as well as radically new string-inspired models, such as the cyclic universe.This research project proposes to explore string cosmology by focusing on the characteristic elements of string theoretic models: string dynamics (typically leading to non-canonical kinetic terms and many relevant light fields), brane dynamics (inter-brane forces, their motion, collision and eventual stabilization), holographic approaches (in particular attempts at understanding the big bang using the AdS/CFT correspondence), violations of the null energy condition (ubiquitous in string cosmology, but not much explored to date) and intersecting brane constructions.These characteristic elements are equally relevant for both inflation and the cyclic universe, and they will therefore be used to identify distinct observational signatures of the string theoretic cosmological models, for example with regard to gravitational waves or the statistics of primordial temperature fluctuations in the cosmic radiation left over from the big bang. Combined with the upcoming precision cosmological data from ground and satellite experiments, this research has the potential to significantly enhance our knowledge of both fundamental theory and cosmology and, therefore, to shed light on the question of the origin and fate of our universe.