  We review the mechanisms of low-temperature electron transport across a
quantum dot weakly coupled to two conducting leads. Conduction in this case is
controlled by the interaction between electrons. At temperatures moderately
lower than the single-electron charging energy of the dot, the linear
conductance is suppressed by the Coulomb blockade. Upon further lowering of the
temperature, however, the conductance may start to increase again due to the
Kondo effect. This increase occurs only if the dot has a non-zero spin S. We
concentrate on the simplest case of S=1/2, and discuss the conductance across
the dot in a broad temperature range, which includes the Kondo temperature.
Temperature dependence of the linear conductance in the Kondo regime is
discussed in detail. We also consider a simple (but realistic) limit in which
the differential conductance at a finite bias can be fully investigated.
