  We argue that the use of the universal unintegrated gluon distribution and
the $k_T$ (or high energy) factorization theorem provides the natural framework
for describing observables at small x. We introduce a coupled pair of evolution
equations for the unintegrated gluon distribution and the sea quark
distribution which incorporate both the resummed leading $ln (1/x)$ BFKL
contributions and the resummed leading $ln (Q^2)$ GLAP contributions. We solve
these unified equations in the perturbative QCD domain using simple parametic
forms of the nonperturbative part of the integrated distributions. With only
two (physically motivated) input parameters we find that this $k_T$
factorization approach gives an excellent description of the measurements of
$F_2 (x,Q^2)$ at HERA. In this way the unified evolution equations allow us to
determine the gluon and sea quark distributions and, moreover, to see the x
domain where the resummed $ln (1/x)$ effects become significant. We use $k_T$
factorization to predict the longitudinal structure function $F_L (x,Q^2)$ and
the charm component of $F_2 (x,Q^2)$.
