The photoionization cross section of metal clusters is studied using simple theoretical models. In the case of small clusters, the plasmon is well below the photoionization threshold and the photoionization is dominated by simple independent-particle processes: One electron absorbs all the energy of the photon and immediately leaves the cluster. For large sodium clusters the photoionization efficiency curve is a result of a two-step process: First, the photon excites a plasmon and then the plasmon decays, either by emitting a photoelectron or by heating the cluster. A simple expression for the photoionization cross section near the threshold is derived. \textcopyright{} 1996 The American Physical Society.