  The physics content of the QGSJET-III Monte Carlo generator of high energy
hadronic collisions is described. In particular, a phenomenological
implementation of higher twist corrections to hard parton scattering processes
is discussed in some detail. Additionally addressed is the treatment of the
so-called ``color fluctuation'' effects related to a decomposition of hadron
wave functions into a number of Fock states characterized by different spatial
sizes and different parton densities. Selected model results regarding the
energy-dependence of the total, elastic, and diffractive proton-proton cross
sections are presented.
