  Recent experiments are reviewed that explore the spin states of a ring-shaped
many-electron quantum dot. Coulomb-blockade spectroscopy is used to access the
spin degree of freedom. The Zeeman effect observed for states with successive
electron number allows to select possible sequences of spin ground states of
the ring. Spin-paired orbital levels can be identified by probing their
response to magnetic fields normal to the plane of the ring and electric fields
caused by suitable gate voltages. This narrows down the choice of ground-state
spin sequences. A gate-controlled singlet--triplet transition is identified and
the size of the exchange interaction matrix element is determined.
