Pendulum suspensions for laser interferometer gravitational wave detectors need to have an extremely highQfactor to minimize Brownian motion noise. In this paper we analyze the limits to theQfactor of the compound pendulum. We show that the observed acoustic loss of niobium can allow pendulumQfactors of 1010to be achieved. This should enable a 3 km terrestrial laser interferometer detector to achieve strain sensitivity of 10−22/&sqrt;Hz at frequencies as low as 10 Hz. At cryogenic temperaturesQfactors up to 1012should be achievable.