  We present a systematic study of twist-3 light-cone distribution amplitudes
of $K^*$ and $\phi$ mesons in QCD. The structure of SU(3)-breaking corrections
is studied in detail. Non-perturbative input parameters are estimated from QCD
sum rules. As a by-product, we update the parameters describing the twist-3
distribution amplitudes of the $\rho$ meson. We also review and update
predictions for the twist-2 distribution amplitudes of $\rho$, $K^*$ and
$\phi$.
