  We review the parton model and the Regge approach to the QCD description of
the deep-inelastic $ep$ scattering at the small Bjorken variable $x$ and
demonstrate their relation with the DGLAP and BFKL evolution equations. It is
shown, that in the leading logarithmic approximation the gluon is reggeized and
the pomeron is a compound state of two reggeized gluons. The conformal
invariance of the BFKL pomeron in the impact parameter space is used to
investigate the scattering amplitudes at high energies and fixed momentum
transfers. The remarkable properties of the Schr\"odinger equation for compound
states of an arbitrary number of reggeized gluons in the multi-colour QCD are
reviewed. The gauge-invariant effective action describing the gluon-Reggeon
interactions is constructed. The known next-to-leading corrections to the QCD
pomeron are discussed.
