Constraints on the space density of extragalactic HVCs

High Velocity Clouds (HVCs) have recently attracted renewed attention with the proposal of their being long lived, massive dark matter dominated clouds of primordial composition distributed throughout the Local Group. In this picture the HVCs would contain a few x 10(7) M. of H I and would be at distances of a few hundred kpc to 1.5 Mpc from the Local Group barycenter. If this extragalactic interpretation of HVCs is true, similar clouds are expected in other galaxy groups and around galaxies. We discuss the limits blind H I surveys and QSO absorption line studies put on this proposed population of clouds