World Summary of $\alpha_s$ (2012)

Determinations of the strong coupling strength, $\alpha_s$, are summarised and a new world average value of $\alpha_s (M_Z)$ is determined, using a new method of pre-averaging results within classes of measurements like hadronic $\tau$ decays, deep inelastic scattering processes, lattice calculations, electron-positron annihilation processes and electro-weak precision fits. The overall result is $$\alpha_s (M_Z) = 0.1184 \pm 0.0007,$$ unchanged from the value obtained in 2009. This presentation is an excerpt from the QCD review section of the 2012 Review of Particle Physics (RPP) of the Particle Data Group.