  We present a consistent theory of superconductive tunneling in single-mode
junctions within a scattering formulation of Bogoliubov-de Gennes quantum
mechanics. Both dc Josephson effect and dc quasiparticle transport in voltage
biased junctions are considered. Elastic quasiparticle scattering by the
junction determines equilibrium Josephson current. We discuss the origin of
Andreev bound states in tunnel junctions and their role in equilibrium
Josephson transport. In contrast, quasiparticle tunneling in voltage biased
junctions is determined by inelastic scattering. We derive a general expression
for inelastic scattering amplitudes and calculate the quasiparticle current at
all voltages with emphasis on a discussion of the properties of subgap tunnel
current and the nature of subharmonic gap structure.
