  This paper is a review of recent lattice QCD results for $D$ and $D_s$ meson
leptonic and semileptonic decays. The theory inputs needed for the
determination of $V_{cd}$ and $V_{cs}$ from experimental results are the meson
decay constants (leptonic decays) and the form factors (semileptonic decays).
In addition one can compare the shape of the form factors from lattice QCD and
experiment, and use the full experimental $q^2$ range (partial decay rates in
$q^2$ bins) to determine the CKM matrix elements.
