Leptonic decays of $B^{-}$ and $D^{-}$mesons

The present status of lattice calculations of f_D, f_B and some mass splittings are discussed. When one includes the uncertainties due to discretization errors, the results do not yet have a sufficient precision to be relevant to phenomenological applications. There are, however, good prospects of cutting down the uncertainties by a factor of 2 or more soon.