  We start from the two existing QCD evolution equations for structure
functions, the BFKL and DGLAP equations, and discuss the theoretical hints for
a unifying picture of the evolution in $x$ and $Q^2.$ The main difficulty is
due to the property of angular ordering of the gluon radiation driving the
evolution and the cancellation of the related collinear singularities. At the
leading $\log\ 1/x$ and leading $\log \ Q^2$ accuracy, we find a unified set of
equations satisfying the constraints.
