I discuss recent results from the numerical CDM simulations concerning the density profiles of galactic halos and the abundance of satellite dark matter halos around galaxies. The models predict 1) halo density distributions that may be too concentrated compared to the density distributions implied by observed galactic rotation curves and 2) ≳5–10 times more satellites than are actually observed around the Milky Way and M31. This may indicate that there are either physical mechanisms at work which complicate the straightforward comparison between observations and dissipationless simulations (e.g., processes that greatly reduce the starformation efficiency in most satellite halos and render them invisible), or that essential physics is missing in the CDM models. ©2001 American Institute of Physics.