Phenomenology From Lattice QCD

I review two subjects in which lattice simulations are making, or can make in the future, a significant contribution to particle physics phenomenology. The first subject is the evaluation of quantities which enter into the determination of the vertex $A$ of the unitarity triangle from experimental measurements of decay rates and mixing amplitudes. These quantities include the form-factors for semileptonic B-decays, the leptonic decay constants of the $B$ and $B_s$ mesons and the $B$-parameters for $B_d$-${\bar{B}}_d$ and $B_s$-${\bar{B}}_s$ mixing and the corresponding parameter for $K$-$\bar{K}$ mixing, $B_K$. In the second part of this talk I will review the status and prospects for the evaluation of $K\to \pi \pi$ amplitudes and for the subsequent study of the $\mathrm{\Delta }I=1\mathrm{/}2$ rule and the evaluation of ${ϵ}^{\mathrm{\prime }}\mathrm{/}ϵ$.