  We analyse the data for the proton structure function $F_2$ over the entire
$Q^2$ domain, including especially low $Q^2$, in terms of perturbative and
non-perturbative QCD contributions. The small distance configurations are given
by perturbative QCD, while the large distance contributions are given by the
vector dominance model and, for the higher mass $q \overline{q}$ states, by the
additive quark approach.
