The carious conditions in which echo-reactions occur have been reviewed. Echo-reactions do not consist of indiscriminate repetition, but depend on personal rapport. The selectivity of echo-reactions, with regard to both the person imitated and the actions repeated, has been demonstrated. The fundamentally social nature of echo-reactions has been pointed out. The tendency of the patients with echo-symptoms to complete automatically sentences and actions initiated by the persons with whom they have established contact has been described. Those completion phenomena are an alternative to, or superimposed on, echo-reactions. The psychological mechanism underlying echo-reactions and the associated completion phenomena is that of identification on a primitive level. The various phases which echolalia and the associated completion phenomenon undergoes in the course of the evolution and re-evolution of speech have been demonstrated. A new interpretation of echo-reactions in schizophrenia has been advanced. They are to be understood, from the psychological point of view, as the result of an impulse to maintain social contact co-existing with the opposing tendency to extreme autism. An unusual case of chronic catatonia has been reported in which echo-reactions existed over many years. This patient, who had been a high grade mental defective, had in the course of his psychosis regressed to a level of speech corresponding to that of low-grade mental deficiency. Echo-reactions in infancy and those occurring under certain condition in normal adults have been discussed. The condition in which echolalia occurs have been found to have in common an urge to speak or act, a tendency to repetition and an incomplete development of impairment of expressive as well as perceptive speech. The conditions for echopraxia are similar but concern motor activity. They echo-reactions have been analysed from the point of view of Gestalt psychology, which throws light on their formal as well as dynamic significance. The pathology and some aspects of the physiology of echo-reactions has been discussed. The part played by the emotional element in their conditioning has been considered in the light of Hughlings Jackson's studies on automatisms.