We investigate decay constants of P and D-wave heavy-light mesons within the mock-meson approach. Numerical estimates are obtained using the relativistic quark model. We also comment on recent calculations of heavy-light pseudo-scalar and vector decay constants. Typeset using REVT E X 1 I. INTRODUCTION Reliable estimates of heavy-light meson decay constants are important, since they appear in many processes from which fundamental quantities can be extracted [1]. Theoretical investigations have focused on estimating decay constants for the weakly decaying pseudo-scalar meson and its HQET (heavy quark effective theory) related vector meson. Whereas the decay constant of the weakly decaying pseudo-scalar meson is of paramount importance for determining fundamental quantities, the decay constant of the S-wave vector meson plays a role in exclusive b ! ul transitions [2] and in radiative leptonic decays of heavy-light mesons [3]. While those decay constants have been and continue to be st...