Despite substantial progress over the past half-century in understanding how galaxies form, important open questions remain regarding how precisely the diffuse gas of the intergalactic medium is converted into stars. One possibility, suggested in recent theoretical models, is that the early phase of galaxy formation involves an epoch when galaxies contain a great amount of gas but are still inefficient at forming stars. Direct proof of such a dark phase has been so far elusive, however—after all, dark galaxies do not emit much visible light. The observational discovery of such galaxies would therefore fill an important gap in our understanding of galaxy evolution.