  We review the peculiarities of transport through a quantum dot caused by the
spin transition in its ground state. Such transitions can be induced by a
magnetic field. Tunneling of electrons between the dot and leads mixes the
states belonging to the ground state manifold of the dot. Unlike the
conventional Kondo effect, this mixing, which occurs only at the
singlet-triplet transition point, involves both the orbital and spin degrees of
freedom of the electrons. We present theoretical and experimental results that
demonstrate the enhancement of the conductance through the dot at the
transition point.
