Magnetism is an elementary consequence of quantum mechanics. Additionally, many fundamental phenomena related to magnetic ordering emerge from fluctuations. Studying spins and their fluctuations in interacting molecular magnets, 2D and 3D magnetic layers and heterostructures and in bulk crystals leads to new insight into fundamental aspects of many-body physics. Electronic and magnonic spin currents represent basic carriers of information which can be tested in transport and by optical means in a broad range of time scales. The fundamentally nonlinear interactions of spins lead to phase transitions, symmetry breaking and surprising switching phenomena that will be investigated.