  A significant fraction of mass in the universe is believed to be in the form
of dark matter (DM). Due to gravitational instability, the DM collapses
hierarchically into DM halos. In this contribution we present a study of the
formation and evolution of such DM halos in a COBE-normalized spatially flat
LCDM model (Omega_0=1-Omega_L=0.3; h=0.7) using high-resolution N-body
simulations. The novelty of this study is use of the newly developed
halo-finding algorithms to study the evolution of both isolated and satellite
(located inside virial radii of larger group- and cluster-size systems) halos.
The force and mass resolution required for a simulated halo to survive in the
high-density environments typical of groups and clusters is high: ~1-3 kpc and
\~10^9 M_sun, respectively. We use the high-resolution Adaptive Refinement Tree
(ART) N-body code to follow the evolution of 256^3 dark matter particles with
dynamic range in spatial resolution of 32,000 in a box of 60/h Mpc.
  We show that the correlation function of these halos is anti-biased with
respect to the dark matter correlation function and is high and steeper than
the correlation function of the isolated virialized objects. The correlation
function evolves only mildly between z=3 and z=1. The mass evolution of
isolated virialized objects determined from the simulation is in good agreement
with prediction of semi-analytical models. The differences exist, however, if
we include satellite halos in the halo catalogs.
