The result of interpreting greatly depends on such psychological states and processes as perception, attention, memory, thinking/cognition, imagination. The complex combination of these phenomena is considered to be the mental mechanism through which any activity including language activity and interpreting as a kind of such activity as mediation is realized. All these phenomena are exercised by the human's mind which, on the one hand, is a functional attribute of any person and, on the other hand, a social specific feature generalized in the development of the society. The development of psychological states and processes is very essential with reference to training and teaching interpreters in specific domains. Some psychological issues of interpreting as a form of mediation and language activity are considered in the paper.