The research group led by R. GRIMM investigates ultracold particle systems consisting of optically trapped quantum gases at temperatures close to absolute zero. Because of their superb experimental accessibility and controllability, such systems represent unique model systems for studies of complex quantum many-body be-havior. This facilitates the investigation of quantum phenomena that are difficult to access in conventional condensed-matter systems. The focus of the present experimental work lies on fermionic particle systems and on few-body quantum systems with tunable interactions.