  We present recent developments on the role of the running coupling constant
at the intersection of perturbative and nonperturbative QCD. A number of
experiments show a smooth transition from small to large scales given by the
four-momentum transfer in the reactions. This is at variance with perturbative
QCD where the running coupling constant becomes infinite when the scale equals
$\Lambda_{{\tiny QCD}}$. Approaches using an effective coupling constant could
help interpret the opposite trend of data as compared to standard perturbative
QCD predictions. We give an overview of the role of the coupling constant in
the procedure to match nonperturbative hadronic model to perturbative QCD and
we propose an extraction of an effective coupling constant from inclusive
electron proton scattering data at large Bjorken x.
