  Microscopic theory of counting statistics of electrical noise is reviewed. We
discuss a model of passive charge detector based on current fluctuations
coupled to a spin, and its relation with the theory of photon counting in
quantum optics. The statistics of tunneling current and, in particular, the
properties of the third moment are studied in detail. The third moment is shown
to be temperature-independent for tunneling in a generic many-body system. Then
the statistics of mesoscopic transport is discussed. We consider applications
of the functional determinant formula for the generating function of counting
distribution to the DC and photo-assisted transport, and to mesoscopic pumping.
A universal dependence of the noise in a mesoscopic pump on the pumping fields
is obtained and shown to provide a method of measuring the quasiparticle charge
in an open system without any fitting parameters.
