  A unified view on macroscopic thermodynamics and quantum transport is
presented. Thermodynamic processes with an exchange of energy between two
systems necessarily involve the flow of other balanceable quantities. These
flows are first analyzed using a simple drift-diffusion model, which includes
the thermoelectric effects, and connects the various transport coefficients to
certain thermodynamic susceptibilities and a diffusion coefficient. In the
second part of the paper the connection between macroscopic thermodynamics and
quantum statistics is discussed. It is proposed to employ not particles, but
'elementary Fermi- or Bose-systems' as the elementary building blocks of ideal
quantum gases. In this way, the transport not only of particles, but also of
entropy can be derived in a concise way, and is illustrated for both ballistic
quantum wires and diffusive conductors. In particular, the quantum interference
of entropy flow is in close correspondence to that of electric current.
