  While the properties of the Kondo model in equilibrium are very well
understood, much less is known for Kondo systems out of equilibrium. We study
the properties of a quantum dot in the Kondo regime, when a large bias voltage
V and/or a large magnetic field B is applied. Using the perturbative
renormalization group generalized to stationary nonequilibrium situations, we
calculate renormalized couplings, keeping their important energy dependence. We
show that in a magnetic field the spin occupation of the quantum dot is
non-thermal, being controlled by V and B in a complex way to be calculated by
solving a quantum Boltzmann equation. We find that the well-known suppression
of the Kondo effect at finite V>>T_K (Kondo temperature) is caused by inelastic
dephasing processes induced by the current through the dot. We calculate the
corresponding decoherence rate, which serves to cut off the RG flow usually
well inside the perturbative regime (with possible exceptions). As a
consequence, the differential conductance, the local magnetization, the spin
relaxation rates and the local spectral function may be calculated for large
V,B >> T_K in a controlled way.
