This thesis sheds new light on the fascinating properties of composite quantum systems.Quantum
systems of different sizes ranging from small bipartite systems to large many-body ensembles
can be studied with the help of modern quantum optical experiments. These experiments make it
possible to observe a broad variety of striking features including nonclassical correlations
complex dynamics and quantum phase transitions. By adopting the complementary perspectives of
quantum information theory quantum chemistry and many-body theory the thesis develops new
methods for the efficient characterization and description of interacting composite quantum
systems.
