Views regarding the conditions of deposition of black shale are reviewed. It is agreed that dearth of oxygen and accumulation of organic matter faster than it can be oxidized are the controlling factors. Black shale faunas are either purely planktonic or mixed planktonic and benthonic. Lithologic differences accompany the two sorts of faunas. The characteristics of these two are considered in detail and the conclusion is reached that the deposition of black shales was not restricted to small areas or to short intervals of time, but that it extended over large areas and continued for long time. The locus was at the deeper levels of the littoral or at the bottom of troughs, in either case where currents could bring in the plankton fauna freely.