Determination of $\Lambda_{\overline{MS}}$ from quenched and $N_f = 2$ dynamical QCD

The scale parameter $\Lambda_{\overline{MS}}$ is computed on the lattice in the quenched approximation and for $N_f = 2$ flavors of light dynamical quarks. The dynamical calculation is done with non-perturbatively $O(a)$ improved Wilson fermions. In the continuum limit we obtain $\Lambda_{\overline{MS}}^{N_f=0} = 243(1)(10)$ MeV and $\Lambda_{\overline{MS}}^{N_f=2} = 217(16)(11)$ MeV, respectively.