  This talk summarizes the quenched calculation of $f_B$ and $f_{B_s}$
presented in hep-lat/9801038. The heavy quark is simulated using an $O(1/M^2)$
improved NRQCD action, and the tadpole improved clover action is used for the
light quarks. The axial current includes the $O(1/M)$ corrections in one-loop
perturbation theory and the $O(1/M^2)$ ones at tree-level. We discuss the
various systematic effects and consistency checks made in the calculation.
