$f_B$ and $f_{B_s}$ using NRQCD

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.