  We discuss the steady-state electronic transport in solid-state and molecular
devices in the quantum regime. The decimation technique allows a comprehensive
description of the electronic structure. Such a method is used, in conjunction
with the generalizations of Landauer's tunneling formalism, to describe a wide
range of transport regimes. We analize mesoscopic and semiclassical metallic
transport, the metal-insulator transition, and the resonant tunneling regime.
The effects of decoherence on transport is discussed in terms of the
D'Amato-Pastawski model. A brief presentation of the time dependent phenomena
is also included.
