  The current world-average of the strong coupling at the Z pole mass,
$\alpha_s(m^2_{Z}) = 0.1181 \pm 0.0013$, is obtained from a comparison of
perturbative QCD calculations computed, at least, at
next-to-next-to-leading-order accuracy, to a set of 6 groups of experimental
observables: (i) lattice QCD "data", (ii) $\tau$ hadronic decays, (iii) proton
structure functions, (iv) event shapes and jet rates in $e^+e^-$ collisions,
(v) Z boson hadronic decays, and (vi) top-quark cross sections in p-p
collisions. In addition, at least 8 other $\alpha_s$ extractions, usually with
a lower level of theoretical and/or experimental precision today, have been
proposed: pion, $\Upsilon$, W hadronic decays; soft and hard fragmentation
functions; jets cross sections in pp, e-p and $\gamma$-p collisions; and photon
F$_2$ structure function in $\gamma\,\gamma$ collisions. These 14 $\alpha_s$
determinations are reviewed, and the perspectives of reduction of their present
uncertainties are discussed.
