  A phenomenological model for the clustering of dark matter halos on the
light-cone is presented. In particular, an empirical prescription for the
scale-, mass-, and time-dependence of halo biasing is described in detail. A
comparison of the model predictions against the light-cone output from the
Hubble Volume $N$-body simulation indicates that the present model is fairly
accurate for scale above $\sim 5h^{-1}$Mpc. Then I argue that the practical
limitation in applying this model comes from the fact that we have not yet
fully understood what are clusters of galaxies, especially at high redshifts.
This point of view may turn out to be too pessimistic after all, but should be
kept in mind in attempting {\it precision cosmology} with clusters of galaxies.
