  Ultracold atomic gases have developed into prime systems for experimental
studies of Efimov three-body physics and related few-body phenomena, which
occur in the universal regime of resonant interactions. In the last few years,
many important breakthroughs have been achieved, confirming basic predictions
of universal few-body theory and deepening our understanding of such systems.
We review the basic ideas along with the fast experimental developments of the
field, focussing on ultracold cesium gases as a well-investigated model system.
Triatomic Efimov resonances, atom-dimer Efimov resonances, and related
four-body resonances are discussed as central observables. We also present some
new observations of such resonances, supporting and complementing the set of
available data.
