Under the title of collective psychology much has been written in recent years in regard to crowds and kindred phenomena of social life. Most that has been written thus far has been based upon general observation and almost no systematic methods exist for the study of this type of social organization. The practical methods which practical men like the political boss, the labor agitator, the stock-exchange speculator, and others have worked out for the control and manipulation of the public and the crowd furnish a body of materials from which it is possible to make a more detailed, a more intimate study of what may be called, in order to distinguish it from that of more highly organized groups, collective behavior. The city, and particularly the great city, in which more than elsewhere human relations are likely to be impersonal and rational, defined in terms of interest and in terms of cash, is in a very real sense a laboratory for the investigation of collective behavior. Strikes and minor revolutionary movements are endemic in the urban environment. Cities, and particularly the great cities, are in unstable equilibrium. The result is that the vast casual and mobile aggregations which constitute our urban populations are in a state of perpetual agitation, swept by every new wind of doctrine, subject to constant alarms, and in consequence the community is in a chronic condition of crisis. What has been said suggests first of all the importance of a more detailed and fundamental study of collective behavior. The questions which follow will perhaps suggest lines of investigation that could be followed profitably by students of urban life. What is the psychology of crisis? What is the cycle of events involved in the evolution of a crisis, political or economic? To what extent may the parliamentary system, including the electoral system, be regarded as an attempt to regularize revolution and to meet and control crises? To what extent are mob violence, strikes, and radical political movements the results of the same general conditions that provoke financial panics, real estate booms, and mass movements in the population generally? To what extent are the existing unstable equilibrium and social ferment due to the extent and speed of economic changes as reflected in the stock exchange? What are the effects of the extension of communication and of news upon fluctuations in the stock market and economic changes generally? Does the scale of stocks on the exchanges tend to exaggerate the fluctuations in the market, or to stabilize them? Do the reports in the newspapers, so far as they represent the facts, tend to speed up social changes, or to stabilize a movement already in progress? What is the effect of propaganda and rumor, in cases where the sources of accurate information are cut off? To what extent can fluctuations of the stock market be controlled by formal regulation?