The theoretical possibilities of communicating through scattering channels are considered in the context of digital communication. Direct-detection, heterodyne, and optimum receivers are discussed and the near optimality of direct-detection systems is noted. It is found that the error probability depends only upon the total received signal energy if certain noise thresholds are exceeded; below these thresholds the performance deteriorates rapidly. It is often difficult to exceed the thresholds with present-day technology, but it should become possible to do so as the technology evolves.